sensors

ArticleArticle IntegratedIntegrated GeoscientificGeoscientific Surveys Surveys at at the the Church Church of of Santa Santa Maria Maria delladella LizzaLizza (Alezio,(Alezio, )Italy)

LaraLara DeDe Giorgi,Giorgi, IvanIvan FerrariFerrari, Francesco, Francesco Giur Giuri,i, Giovanni Giovanni Leucci Leucci * and * and Giuseppe Giuseppe Scardozzi Scardozzi

InstituteInstitute ofof HeritageHeritage Science,Science, National National Research Research Council Council of of Italy, Italy, 73100 73100 , Lecce, Italy; Italy; [email protected] [email protected] (L.D.G.); [email protected](L.D.G.); [email protected] (I.F.); [email protected] (I.F.); francesco.giur (F.G.);[email protected] [email protected] (F.G.); [email protected] (G.S.) (G.S.) ** Correspondence: Correspondence: [email protected]; [email protected]; Tel.: Tel.: +39-083-242-2213 +39-083-242-2213

Abstract:Abstract: TheThe churchchurch ofof SantaSanta MariaMaria delladella LizzaLizza isis oneone ofof thethe mostmost importantimportant examplesexamples ofof medievalmedieval architecturearchitecture inin thethe SalentoSalento PeninsulaPeninsula inin southsouth Italy.Italy.In Inorder orderto tounderstand understandthe theextension extensionand andlayout layout ofof thethe crypts,crypts, integratedintegrated ground-penetratingground-penetrating radarradar (GPR)(GPR) prospectionsprospections andand laserlaser scannerscanner surveyssurveys werewere undertakenundertaken in in thethe churchchurch andand inin thethe surroundingsurrounding areas.areas. TheThe analysisanalysis ofof thethe GPRGPR measurementsmeasurements revealedrevealed manymany anomaliesanomalies thatthat couldcould bebe ascribedascribed toto unknownunknown structuresstructures (crypts),(crypts), asas wellwell asas otherother anomaliesanomalies related to to the the old old church. church. The The GPR GPR data data were were supported supported by the by laser the laserscanner scanner data estab- data establishinglishing the spatial the spatial relationship relationship between between the surface the surface and andthe level the level below below the church. the church.

Keywords:Keywords: GPR;GPR; laserlaser scanner;scanner; SantaSanta MariaMaria delldell LizzaLizza church;church; AlezioAlezio (Italy)(Italy)

1.1. IntroductionIntroduction   TheThe churchchurch of of Santa Santa Maria Maria della della Lizza Lizza in in Alezio Alezio (Figure (Figure1) is1) ais very a very important important example exam- Citation: De Giorgi, L.; Ferrari, I.; ofple late of medievallate medieval religious religious architecture architecture in the in the Apulia region region in southern in southern Italy. Located Italy. Located on the Citation:Giuri, F.; DeLeucci, Giorgi, G.; L.;Scardozzi, Ferrari, I.;G. westernon the western side of theside of the peninsulaSalento peninsula about 6.5 ab kmout east 6.5 ofkm Gallipoli, east of Gallipoli, with its high with turreted its high Giuri,Integrated F.; Leucci, Geoscientific G.; Scardozzi, Surveys G. at pronaosturreted it pronaos dominates it dominates a vast territory a vastprojected territory projected onto the Ionian onto the Sea Ionian (Figure Sea2). (Figure The building 2). The Integratedthe Church Geoscientific of Santa Maria Surveys della at is linked to the ancient cult of the Assumption of Mary, defined as “della Lizza” or “di the Church of Santa Maria della Lizza building is linked to the ancient cult of the Assumption of Mary, defined as “della Lizza” Lizza (Alezio-Italy). Sensors 2021, 21, Alizza” because it was built on the homonymous hill, characterized by a toponym that (Alezio,x. https://doi.org/10.3390/xxxxx Italy). Sensors 2021, 21, 2205. or “di Alizza” because it was built on the homonymous hill, characterized by a toponym derives from the ancient Messapian-Roman settlement of Aletium, in which the Lizza hill https://doi.org/10.3390/s21062205 that derives from the ancient Messapian-Roman settlement of Aletium, in which the Lizza was one of the most important sectors [1]. Academic Editor: Francesca Cigna hill was one of the most important sectors [1]. Academic Editor: Francesca Cigna Received: 23 February 2021 Received:Accepted: 23 18 February March 2021 2021 Accepted:Published: 18 21 March March 2021 2021 Published: 21 March 2021 Publisher’s Note: MDPI stays Publisher’sneutral with Note: regardMDPI to jurisdictional stays neutral withclaims regard in topublished jurisdictional maps claims and in publishedinstitutional maps affiliations. and institutional affil- iations.

Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Copyright: © 2021 by the authors. This article is an open access article Licensee MDPI, Basel, Switzerland. distributed under the terms and This article is an open access article conditions of the Creative Commons distributed under the terms and Attribution (CC BY) license conditions of the Creative Commons (http://creativecommons.org/licenses FigureFigure 1.1. Church of Santa Maria della Lizza in Alezio (Lecce, Italy). South-west view of the high Attribution (CC BY) license (https:// Church of Santa Maria della Lizza in Alezio (Lecce, Italy). South-west view of the high /by/4.0/). turreted pronaos. creativecommons.org/licenses/by/ turreted pronaos. 4.0/).

Sensors 2021, 21, x. https://doi.org/10.3390/xxxxx www.mdpi.com/journal/sensors Sensors 2021, 21, 2205. https://doi.org/10.3390/s21062205 https://www.mdpi.com/journal/sensors SensorsSensors2021 2021, 21, 21, 2205, x FOR PEER REVIEW 22 of of 17 17

FigureFigure 2. 2.Church Church of of Santa Santa Maria Maria della della Lizza Lizza in in Alezio Alezio (Lecce, (Lecce, Italy). Italy). Aerial Aerial view view from from the the north-east. north- east. The church underwent various construction phases, which over time have strongly alteredThe its church appearance. underwent The original various layoutconstruction is presumably phases, datablewhich over to between time have the strongly end of thealtered 13th its and appearance. the beginning The of original the 14th layout century. is presumably It was characterized datable to by between a Latin crossthe end plan of outlinedthe 13th givenand the by beginning the intersection of the of14th the century. nave and It thewas apsed characterized presbytery by (about a Latin 30 cross× 10 plan m) withoutlined a monumental given by the strongly intersection projecting of the transept nave and (about the apsed 21 × 8 presbytery m), externally (about embellished 30 × 10 m) withwith raiseda monumental pilasters strongly which, branching projecting off transept from the(about plinth 21 at× 8 the m), bottom, externally rejoin embellished curving upwardswith raised to form pilasters elegant which, trefoil branching arches [2 ,off3]. fr Moreom the properly plinth assignable at the bottom, to the rejoin 14th centurycurving isupwards the construction to form elegant of the monumentaltrefoil arches turreted[2,3]. More pronaos properly (18 as msignable high) leaning to the 14th against century the entranceis the construction of the church, of the open monumental with pointed turre archested onpronaos three sides(18 m and high) vaulted leaning with against a ribbed the cruise.entrance This of isthe a raritychurch, in open the panorama with pointed of medieval arches on architecture three sides of and the vaulted Italian peninsulawith a ribbed [4]. Startingcruise. This from is the a 16thrarity century in the andpanorama up to the of 19thmedieval century architecture at the behest of ofthe various Italian bishops peninsula of Gallipoli,[4]. Starting the churchfrom the was 16th the century subject ofand heavy up to building the 19th interventions century at the that behest transformed of various the austerebishops and of Gallipoli, slender medieval the church appearance was the subject internally of heavy embellished building with interventions colorful frescoes that trans- [5], intoformed a building the austere of worship and slender with medieval typically appear baroqueance connotations. internally embellished The roof with with wooden colorful trussesfrescoes was [5], replacedinto a building by cross of worship vaults in with masonry typically supported baroque connot by mightyations. pillars The roof leaning with againstwooden the trusses walls was of the replaced nave and by cross transept, vaults which in masonry together supported with the richby mighty and majestic pillars Baroqueleaning altarsagainst obliterated the walls theof the ancient nave frescoes. and tran Thesept, old which single-lancet together windows with the wererich and bricked ma- upjestic and Baroque new ones altars were obliterat made byed forcibly the ancient cutting frescoes. into the The walls. old Asingle-lancet new nave was windows built on were the northernbricked up front and adjacent new ones to thewere central made one by andforcib connectedly cutting with into twothe walls. large andA new high nave arched was openingsbuilt on the in thenorthern walls, front plus aadjacent third to to the the east central that gaveone and access connected to the northern with two branch large and of thehigh transept. arched openings The room in used the walls, as a sacristy plus a thir wasd set to the against east thethat north gave access front of to the the transept, northern whilebranch the of bishop’sthe transept. palace The occupied room used the as corner a sacristy between was theset transeptagainst the and north the presbytery,front of the thetransept, point where while the bellbishop’s tower palace also stood; occupied on the the southern corner between external the front transept of the pronaosand the pres- and aislebytery, and the up point to the where transept the was bell the towerCappellone also stood;of the on Congrega the southern (Figure external3). Probably front of as the a resultpronaos of alland these aisle interventions, and up to the towards transept the was first the half Cappellone of the 20th of century the Congrega the church (Figure began 3). toProbably show more as a andresult more of all evident these interventions, signs of structural towards failure, the first which half lead of the to 20th the impressive century the and questionable restorations of the years 1959–1961. In this circumstance, a conservative church began to show more and more evident signs of structural failure, which lead to the intervention was not pursued, but a stylistic restoration that eliminated all the baroque impressive and questionable restorations of the years 1959–1961. In this circumstance, a evidence to give the building its original appearance again. conservative intervention was not pursued, but a stylistic restoration that eliminated all the baroque evidence to give the building its original appearance again.

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FigureFigure 3. 3.Church Church of of Santa Santa Maria Maria della della Lizza Lizza in in Alezio Alezio (Lecce, (Lecce, Italy). Italy). Photographic Photographic document document from from the earlythe early 20th 20th century century thatstill that shows: still shows: the masonry the masonry vaults vaults (a), the (a small), the northernsmall northern nave (b nave), the ( sacristyb), the (c), sacristy (c), the bishop’s palace (d), the bell tower (e), the Congrega’s house (f) and buildings lean- the bishop’s palace (d), the bell tower (e), the Congrega’s house (f) and buildings leaning against the ing against the pronaos (g) (after [6]). pronaos (g) (after [6]).

InIn thisthis wayway thethe trussestrusses werewere restored,restored, inin thethe presbytery presbytery thethe pointedpointed archarch withwith the the upperupper choirchoir and the apse behind behind it it was was rebuilt, rebuilt, the the pointed pointed arches arches at atthe the intersection intersection be- betweentween the the nave nave and and the the transept transept were were also also rebuilt, rebuilt, the thewalls walls in the in damaged the damaged portions portions were wererepaired, repaired, reopened reopened the original the original doors doors and andwindows windows and andfinally finally brought brought to light to light the thesur- survivingviving frescoes. frescoes. These These restoration restoration works works involved involved the theinternal internal demolition demolition of vaults, of vaults, pil- pillars,lars, altars altars and and any any other other sacred sacred furnishings, furnishings, while while externally, externally, with with the the exception exception of the of theepiscope, episcope, the theCongrega’s Congrega’s house, house, the thesmall small northern northern nave, nave, the theold oldsacristy sacristy and and the thebell belltower tower were were also also demolished, demolished, plus plus further further buildings buildings built built at the at turn the turn of the of 19th the 19th and and20th 20thcenturies centuries close close to the to pronaos the pronaos [7]. It [ 7was]. It during was during these theseworks works that the that rooms the roomsof the ofunder- the undergroundground cemetery cemetery below below the church the church were discov were discovered,ered, due to duethe subsidence to the subsidence of the floor of the in floorthe north in the arm north of the arm transept. of the transept. It consists It consistsof a series of of a small series rooms, of small independent rooms, independent from each fromother, each built other, in square built blocks in square of local blocks stone of and local barrel stone vaulted, and barrel whose vaulted, only access whose points only accesswere quadrangular points were quadrangular entrances of 60/80 entrances cm side, of placed 60/80 cmin the side, floor placed of the in church the floor and ofclosed the churchby removable and closed tombstones: by removable through tombstones: this opening through alone this the opening dead were alone lowered the dead into were the loweredunderground into the rooms underground for their burial. rooms In for the their first burial.centuries In after the first Christ, centuries the practice after Christ,of bur- theials practice ad sanctos of burialsor martyribusad sanctos sociatusor martyribus was instituted sociatus towas facilitate instituted the path to facilitate of the thedeceased path oftowards the deceased the resurrection. towards the During resurrection. the Medieval During and the post-Medieval Medieval and times, post-Medieval the nobles times, were thedeposited nobles werein underground deposited in rooms underground located near rooms or locatedin front near of family or in chapels; front of family the clergymen, chapels; theon clergymen,the other hand, on the were other buried hand, in werea single buried underground in a single room, underground located near room, the located presbytery near theand presbytery the main altar; and the maincommoners altar; the were commoners piled without were a piledcoffin, without wrapped a coffin,only in wrapped a shroud, onlyand deposited in a shroud, in andseveral deposited underground in several corridors underground under the corridors main nave. under This the type main of nave.hypo- Thisgeum type cemetery of hypogeum had an important cemetery hadtradition an important in Christian tradition Salento in (as Christian for example Salento document (as for examplethe important document cases thein the important cathedrals cases of Lecce in the and cathedrals Nardò) and of Lecce was adopted and Nard untilò) and the early was adopted19th century, until thewhen early after 19th the century, Napoleonic when edic aftert of the Saint Napoleonic Cloud for edict hygienic of Saint and Cloud sanitary for hygienicreasons, andburial sanitary in urban reasons, centers burial was in forbidden urban centers to relegate was forbidden it to special to relegate extra-urban it to special areas. extra-urbanDespite this, areas. the Aletine Despite this,community the Aletine continue communityd to bury continued their dead to bury in theirthe Lizza dead under- in the Lizzaground underground cemetery until cemetery the second until thehalf second of the 19th half ofcentury. the 19th century. ThisThis contributioncontribution aimsaims toto illustrateillustrate thethe resultsresultsachieved achievedby bythe the joint joint research research activity activity ofof thethe InformationInformation TechnologiesTechnologies LaboratoryLaboratory (ITLab)(ITLab) andand thethe LaboratoryLaboratory ofof AppliedApplied Geo-Geo- physicsphysics of of the the Institute Institute of of Heritage Heritage Sciences Sciences (ISPC) (ISPC) of theof the CNR CNR of Lecce of Lecce (south (south Italy), Italy), in the in contextthe context of a widerof a wider scientific scientific collaboration collaboration project project stipulated stipulated with the with Municipality the Municipality of Alezio of (LecceAlezio Province) (Lecce Province) and the and Salento the Salento University, University, with the with cooperation the cooperation of the Archaeologicalof the Archaeo- Superintendence.logical Superintendence. The investigations The investigations involved involved the Church the of Church Santa Maria of Santa della Maria Lizza della and more specifically the underground rooms located below the building and the surrounding Lizza and more specifically the underground rooms located below the building and the

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area. Although the discovery of the underground rooms dates back to about sixty years ago, a plan of the hypogeum cemetery has never been published. However, it is an essential element to understand (i) the real extension and distribution of the underground rooms and their relationship with the structures of the church, and (ii) the dimensions of the individual compartments and the spatial relationship between them. Therefore, accord- ing to a working methodology already adopted in other research activities performed in cooperation by the two laboratories [8–10], in some cases also conducted on the same territory [11], laser scanning surveys and ground-penetrating radar (GPR) investigations were carried out to fill the gap in the knowledge of this context. The laser scanning surveys were aimed at producing a 3D model of the church, including the external churchyard and the underground rooms. Some graphic tables have been created, which have been very useful in the examination of some technical- construction details of the monument, especially linked to the different construction phases. Furthermore, the survey was preparatory to the planning of the GPR prospecting campaign that has allowed for the identification of structures unknown until now, both inside and outside the church, fundamental to offer a more organic knowledge and understanding of the transformations of a monument still little studied.

2. Materials and Methods 2.1. Laser Scanner Survey Laser scanner survey was performed using a Leica P20 instrument ((Leica, Wetzlar, Germany). The coverage of the entire underground area was achieved by planning a total of 40 station points, including part of the external area facing the two underground entrances for a precise connection to the church structures: due to the small size of the rooms, but above all due to the absence of relevant decorative details, it was set a resolution of 12.5 mm on a sphere of 10 m of radius, quality three. The measurement resolution chosen made it possible to have an easily manageable amount of data considering the numerous points of stations planned at regular intervals for the total coverage of the area. For processing data has been used a workstation equipped with an Intel Xenon ES-2630 2.30 GHz processor, 32 GB of RAM and an Nvidia K 4000 graphics card. The acquired data were first processed in Cyclone software (v 8.1.1, Leica, Wetzlar, Germany) to align the point clouds and to export them in a single .pts file of 11 GB with 352 million points. Subsequently the points were decimated in Geomagic (v Studio 2003, Morrisville, NA, USA) to get a polygonal mesh with a good level of detail easy to manage: the 3D model of 4.1 million of polygons was exported in .obj file of about 200 MB. The same workflow was used for a 3D laser scanner survey of the church and the external churchyard. To cover the entire area, 78 additional station points were necessary, and to ensure a good degree of accuracy of the high portions it was adopted an instrument resolution of 6.3 mm on a sphere of 10 m radius. The exported .pts file of 32.4 GB has about 1.3 billion points; from it a 3D .obj model of 590 MB of about 65 million polygons was processed, and it is divided into eight parts of 5 million polygons each for the church and a further 5 parts of 5 million each for the churchyard. All these models were finally imported and merged into Maxon C4D (v R14.014) for the creation of plans, sections and rendering (Figure4). Sensors 2021, 21, 2205 5 of 17 Sensors 2021, 21, x FOR PEER REVIEW 5 of 17

FigureFigure 4. 4.Screenshot Screenshot of of the the survey survey campaign campaign data data processing: processing: ( a(a)) the the 1.3 1.3 billion billion point point cloud; cloud; ( b(b)) the the polygonal surface processed from the point cloud; (c) the model optimization and the creation of polygonal surface processed from the point cloud; (c) the model optimization and the creation of plans, sections and renderings. plans, sections and renderings.

2.2.2.2. GPR GPR Data data Acquisition AA GPRGPR survey was was performed performed on on six six areas areas labelled labelled Area Area 1-Area 1-Area 6, respectively 6, respectively (Figure (Figure5): Area5): 1 Area is an 1 open is an space open spaceimmediately immediately to the to north the north of the of church, the church, corresponding corresponding to the todemolished the demolished northern northern nave naveand old and sacristy old sacristy (see (seeSection Section 2 above);2 above); Area Area 2 is 2 isinside inside the thechurch, church, including including the thetransept transept and and the thenave; nave; Area Area 3 is 3inside is inside the pronaos; the pronaos; Area Area 4 is an 4 isopen an open space space immediately immediately south south of the of pronao the pronaoss and the and nave, the nave,corresponding corresponding to the demol- to the demolishedished Congrega’s Congrega’s house house (see above (see above paragraph paragraph 2); Area 2); Area5 is a 5small is a small open openspace space south south of the oftransept; the transept; Area 6 Area is an 6 open is an space open in space front in of front the pronaos, of the pronaos, partially partially corresponding corresponding with the withnorthern the northern sector of sectorthe demolished of the demolished housing (see housing above (see paragraph above paragraph 2). For the 2). GPR For meas- the GPRurements measurements the georadar the georadarRis Hi-Mod Ris was Hi-Mod used. was with used. the withaim of the obtaining aim of obtaining a good compro- a good compromisemise between between resolution resolution and depth and of depth investig ofation, investigation, the dual theband dual antenna band was antenna used waswith

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usedcentral with band central frequencies band frequencies equal to 200 equal and 600 to 200MHz. and GPR 600 data MHz. were GPR acquired data were with acquired parallel withprofiles parallel spaced profiles 25 cm. spaced Successively 25 cm. Successivelydata were processed data were by processed the follow by steps: thefollow (i) zero steps: tim- (i) zero timing; (ii) background removal filter [12]; (iii) gain variable versus depth [13]; ing; (ii) background removal filter [12]; (iii) gain variable versus depth [13]; (iv) Kirchoff (iv) Kirchoff migration [13]. For this last step the electromagnetic wave propagation velocity migration [13]. For this last step the electromagnetic wave propagation velocity of 0.11 of 0.11 m/ns, evaluated from diffraction hyperbolas [13], was used. m/ns, evaluated from diffraction hyperbolas [13], was used.

Figure 5. The GPR surveyed areas with location of some profiles.profiles.

The GPR-slice GPR-slice software software [14] [14 ]was was used. used. The The GP GPRR data data analysis analysis show show that thatonly onlythe data the dataobtained obtained from fromthe 600 the MHz 600 MHz antenna antenna were were significative significative and andtherefore therefore only only the thedata data ob- obtainedtained from from 600 600 MHz MHz will will be be analyzed analyzed here. here. After After appropriate appropriate data data processing, various three-dimensional visualizationvisualization techniquestechniques are are currently currently used used to to display display the the GPR GPR data data in in a convenienta convenient way way for for understanding understanding the spatialthe spatial relationships relationships between between the anomalous the anomalous zones andzones improving and improving their archaeological their archaeological interpretation. interpretation. The most The popularmost popular GPR visualizationGPR visuali- methodzation method is as time-slice is as time-slice (or depth-slice) (or depth-slice) maps [15 –maps17] since [15–17] it provides since it a comprehensiveprovides a compre- plan viewhensive of theplan anomaly view of the patterns anomaly at various patterns depths, at various easy depths, to correlate easy withto correlate structures with within struc- increasinglytures within deeperincreasingly archaeological deeper archaeological units. This is a units. useful This that is creates a useful maps that of creates reflected maps wave of amplitudereflected wave differences amplitude indiscreet differences horizontal in discreet time horizontal slices within time a slices grid [within18–23]. a This grid type[18– of23]. visualization This type of playsvisualization an important plays rolean important in unravelling role in the unravelling complex layers the complex within urbanlayers settingswithin urban and the settings evolution and the of buildings evolution and of bu urbanildings landscapes and urban through landscapes time [through18,19,24 –time26]. Amplitude[18,19,24–26]. slice-maps Amplitude were slice-maps constructed were using constr theucted overlay using analysis the overlay [17]. analysis This allow [17]. to This the strongestallow to the and strongest weakest and reflectors weakest at thereflectors depth at of the each depth slice of are each assigned slice are specific assigned colours specific and thereforecolours and allow therefore to see theallow subtle to see features the subtle that features are indistinguishable that are indistinguishable on radargrams. on radar- grams. 3. Results 3.1. Laser Scanner 3. Results The plan obtained by instrumental survey was compared with the only one published 3.1. Laser Scanner to date [7]. Differences emerged both in the metric accuracy and in the alignment of the structures.The plan For obtained this reason, by instrumental an attempt wassurvey made was to compared combine thewith instrumental the only one survey pub- withlished the to olddate technical [7]. Differences drawing emerged showing both the in plans the ofmetric the demolishedaccuracy and buildings, in the alignment this not consideringof the structures. the whole For this of reason, the drawing, an attemp but analyzingt was made separately to combine those the instrumental of the individual sur- buildingsvey with the to minimizeold technical the percentagedrawing showing of relative the error. plans of the demolished buildings, this not consideringBy analyzing the thewhole 3D of model the drawing, of the underground but analyzing sector, separately it is possiblethose of the to clearlyindividual un- derstandbuildings theto minimize size of the the individual percentage rooms, of relative their error. location, the levels and the path of the modernBy analyzing corridors createdthe 3D model during of the the 1959–1960 undergroun restorationsd sector, toit is provide possible a tourist to clearly visit under- route. Thestand underground the size of the rooms individual are accessible rooms, their by lo acation, staircase the placed levels and in the the entrance path of the hall modern of the corridors created during the 1959–1960 restorations to provide a tourist visit route. The

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undergroundunderground rooms rooms are areaccessible accessible by aby staircase a staircase placed placed in the in theentrance entrance hall hall of the of thebishop’s bishop’s bishop’s palace, which leads into a passage 70 cm wide and 2.60 m height. The corridor, palace,palace, which which leads leads into into a passage a passage 70 cm 70 cmwide wide and and 2.60 2.60 m height. m height. The The corridor, corridor, after after a first a first after a first stretch to west direction, turns 90◦ to the south, passes the foundations in the stretchstretch to west to west direction, direction, turns turns 90° 90°to the to thesouth, south, passes passes the thefoundations foundations in the in thenorth north wall wall of thenorth transept wall of and the lead transept to the and first lead series to the of firstfour series funerary of four cells funerary placed cellsbelow placed the transept below the transeptof the transept (Figure and6, I–IV). lead to the first series of four funerary cells placed below the transept (Figure(Figure 6, I–IV). 6, I–IV).

FigureFigureFigure 6. General 6.6.General General plan, plan,plan, from fromfrom laser laser laser scanner scanner scanner survey, survey, survey, showing showing showing the the undergroundthe underground underground rooms rooms rooms documented documented documented by by laserby laser scanner scanner and and the sectionthe section lines lines of Figure of Figure 10. 10.

TheTheThe lateral laterallateral rooms roomsrooms I and II andand IV IVareIV are arelarger, larger,larger, have have have an an almostan almost almost specular specular specular polygonal polygonal polygonal plan planplan and andand originallyoriginallyoriginally both both both had had had a adepressed a depressed depressed barrel barrel barrel vault vault vault with with with an east-westan east-west axis:axis: axis: todaytoday today the the northern thenorthern northern one onehasone has a has a flat flat a concrete flatconcrete concrete modern modern modern roof roof builtroof built built in in the the in 1959–1961 the1959–1961 1959–1961 restoration restoration restoration due due thedue the collapse thecollapse collapse of of the of thechurch thechurch church floor floor floor in in this this in pointthis point point (Figure (Figure (Figure7a). 7a). The 7a). The trap The trapdoor trap door indoor in room room in room I located I located I located on on the theon southern thesouthern southern side sideisside is sealed, sealed, is sealed, unlike unlike unlike that that of that of room room of room IV IV placed placedIV placed on on the theon western thewestern western side side and side and protected and protected protected by aby metal aby metal a grate:metal grate:thisgrate: this is onethis is one is of one theof the of three thethree trapthree trap doors trap doors doors opened open opened during duringed during the the restoration therestoration restoration for for thethefor GreattheGreat Great Jubilee Jubilee in in 2000,in 2000, when when the theLizza Lizza sanctuary sanctuary was was celebratedcelebrated celebrated itsits jubilee jubileeits jubilee stage.stage. stage. ByBy comparing comparingBy comparing thethe currentthecur- cur- rentdatarent data withdata with with those those those of of the the of church thechurch church in in the the in Baroque theBaroque Baroqueperiod, period, period, wewe understandweunderstand understand how how the thepresence presence of of theof thealtars altars altars of of St. St.of CharlesSt. Charles Charles Borromeo Borromeo Borromeo on on theon the thenorth north north and and and the the theCrucifix Crucifix Crucifix on on theon the thesouth south south have have have led led led thethe thecells cellscells to be toto bebuiltbe builtbuilt away awayaway from from from the the theback back back wall walls walls ofs ofthe of the thetransept. transept. transept. It also ItIt also also understood understood understood how how how the the the particularparticularparticular plan planplan shape shapeshape was waswas linked linkedlinked to the toto the thepresen presencepresence ofce theof of the thepillars pillarspillars supportingsupporting supporting the the thecross cross cross vaults vaults vaults andandand the the theneed needneed to avoid toto avoidavoid gaps gapsgaps undermining underminingundermining the the thestability stability stability of the of of the thebuilding building building (Figure (Figure (Figure 8).8 ).8).

Figure 7. Underground rooms: (a) sepulchral cell I; (b) sepulchral cell III. FigureFigure 7.7.Underground Underground rooms:rooms: ((aa)) sepulchralsepulchral cell cell I; I; ( b(b)) sepulchral sepulchral cell cell III. III.

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FigureFigure 8.8. The new general general plan plan laser laser scanning scanning survey survey integrated integrated with with the the plans plans of ofthe the buildings buildings demolisheddemolished duringduring thethe 1959–19611959–1961 restorationsrestorations fromfrom MongielloMongiello 1974. 1974.

TheThe twotwo smallersmaller centralcentral roomsrooms (II(II andand III)III) areare almostalmost alignedaligned withwith eacheach otherother onon anan axis,axis, havehave aa rectangularrectangular planplan andand depresseddepressed barrelbarrel vaultsvaults withwith anan east-westeast-west axis.axis. TheThe traptrap doordoor ofof roomroom IIIIII locatedlocated inin thethe north-westnorth-west cornercorner isis sealedsealed (Figure(Figure7 b),7b), while while the the one one in in roomroom IIII locatedlocated inin thethe south-westsouth-west cornercorner isis openopen andand protectedprotected byby aa grate:grate: thisthis lastlast roomroom waswas thethe mostmost importantimportant oneone byby itsits positionposition inin frontfront ofof thethe mainmain altar,altar, herehere thethe clericalclerical exponentsexponents werewere buried.buried. TheThe twotwo smaller smaller central central rooms rooms (II (II and and III) III) are almostare almost aligned aligned on an on axis an with axis eachwith other, each haveother, a have rectangular a rectangular plan and plan depressed and depressed barrel vaultsbarrel vaults with an with east-west an east-west axis. The axis. trap The door trap ofdoor room of IIIroom located III located in the north-westin the north-west corner iscorn sealeder is (Figuresealed 7(Figureb), while 7b), the while one in the room one IIin locatedroom II inlocated the south-west in the south-west corner is corner open and is op protecteden and protected by a grate: by thisa grate: last roomthis last was room the mostwas the important most important one by its one position by its in position front of in the front main of altar, the main here thealtar, clerical here exponentsthe clerical wereexponents buried. were buried. From the room IV a new corridor moves toward west through an opening in the From the room IV a new corridor moves toward west through an opening in the foundations of the transept wall, and with a short staircase it is possible to descend further foundations of the transept wall, and with a short staircase it is possible to descend further 1.2 m. After six meters, a branch of the visit path turns 90◦ northwards and oversteps the 1.2 m. After six meters, a branch of the visit path turns 90° northwards and oversteps the southern wall of the nave: here is a second group of further four cells (Figure6, V–VIII) southern wall of the nave: here is a second group of further four cells (Figure 6, V–VIII) reaching by going up four steps and having all a rectangular plan with a depressed barrel reaching by going up four steps and having all a rectangular plan with a depressed barrel vault on the north-south axis. The southern rooms (V and VII) have their own trap doors vault on the north-south axis. The southern rooms (V and VII) have their own trap doors on their southern sides plus a third in the middle communicating with both: among these, on their southern sides plus a third in the middle communicating with both: among these, the western one is the third that was reopened and protected by a metal grate in 2000 the western one is the third that was reopened and protected by a metal grate in 2000 (Figure9a). The couple of northern rooms (VI and VIII) have instead their respective trap (Figure 9a). The couple of northern rooms (VI and VIII) have instead their respective trap doors each on the northern side (Figure9b). Also in this case, by superimposing the current doors each on the northern side (Figure 9b). Also in this case, by superimposing the cur- plan on that of the Baroque building, we see how the three southern trap doors touch therent three plan sideson that of of the the podium Baroque of building, the demolished we see how altar the of three the Madonna southernof trap Good doors Advice. touch Reversingthe three sides this observation of the podium on the of the two demolis northernhed hatches, altar of it the is easy Madonna to suppose of Good an identical Advice. andReversing specular this situation observation relating on tothe an two altar northern no longer hatches, existing it inis theeasy 20th to suppose century, butan identical present beforeand specular the construction situation relating of the small to an northern altar nonave longer (Figure existing8). in the 20th century, but pre- sent before the construction of the small northern nave (Figure 8).

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FigureFigure 9.9.Underground Underground rooms:rooms: ((aa)) thethe sepulchralsepulchral cell cell VI; VI; ( b(b)) the the sepulchral sepulchral cell cell VII. VII.

AnalyzingAnalyzing thethe differentdifferent sectionssections ofof thethe 3D3D model,model, wewe cancan seesee howhow thethe floorsfloors ofof thethe eighteight funeralfuneral cellscells are are at at a a depth depth between between− −2.602.60 andand −−2.85 m from the floorfloor of thethe church.church. TheThe vaults vaults reach reach a a thickness thickness of of only only 25 25 cm cm at theat the highest highest points points (Figure (Figure 10). 10). Small Small ventilation ventila- ductstion ducts in the in walls the allowedwalls allowed for the for circulation the circulation of gases of from gases the from decomposition the decomposition of corpses of andcorpses their and expulsion their expulsion outside for outside air exchange. for air exchange.

Figure 10. Sections of the underground rooms from laser scanner survey (general plan Figure 6). FigureFigure 10.10.Sections Sections ofof thethe undergroundunderground rooms rooms from from laser laser scanner scanner survey survey (general (general plan plan Figure Figure6 ).6).

ComingComing backback to the east-west corridor, corridor, a a pa passagessage on on the the south south side side lead lead to to a alarge large L- L-shapedshaped cistern cistern covered covered by by a depressed a depressed barrel barrel vault vault with with a north-south a north-south axis axis (Figure (Figure 5, IX),5, IX),which which probably probably pre-existed pre-existed the the construction construction of of the the Congrega’s Congrega’s house house because ofof partlypartly extendedextended belowbelow itsits southernsouthern wallwall (Figure (Figure 11 11a).a).

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FigureFigure 11. 11.Underground Underground rooms: rooms: ( (aa))) the thethe cistern cisterncistern (IX); (IX);(IX); ( (b(b))) the thethe food foodfood warehouse warehousewarehouse (XI). (XI).(XI).

PreciselyPrecisely forfor this this reason, reason, it itis islikely likely that that the thecistern cistern originally originally had a had square a square plan, which plan, whichwas then was modified then modified to give toa masonry give a masonry base to the base building’s to the building’s pillar putted pillar in puttedthe south-east in the south-eastcorner (Figure corner 8). (Figure A further8). Aelement further that element emerged that from emerged a rare from photographic a rare photographic document documenttakentaken duringduring taken thethe during demolitiondemolition thedemolition ofof thethe buildingbuilding of the isis buildingthethe presencepresence is the ofof presenceaa largelarge archarch of ainin large thethe southernsouthern arch in thewall southern of the Congrega’s wall of the house Congrega’s right above house the right ci abovestern: a the technical cistern: solution a technical that solution allowed that the allowedweight of the the weight structure of the to structureunload not to directly unload noton itsits directly vault,vault,on butbut its ratherrather vault, laterallylaterally but rather toto itit laterally (Figure(Figure to12). it (FigureThe mouth 12). Theof the mouth tank of for the gathering tank for gatheringrain waters rain has waters a quadrangular has a quadrangular shape (50 shape × 50 × (50cm); it50 is cm); along it is the along median the median axis near axis the near cistern the cistern on southern on southern side, side,exactly exactly placed placed in line in linewith with the theinternal internal curtain curtain wall wall of the of thedemolished demolished building. building.

Figure 12. Photographic document from 1960 showing the Congrega’s house demolishment: the FigureFigure 12. 12.Photographic Photographic document document from from 1960 1960 showing showing the the Congrega’s Congrega’s house house demolishment: demolishment: the the red red arrow points to the arch above the cistern. arrowred arrow points points to the to arch the abovearch above the cistern. the cistern.

TheThe penultimatepenultimate roomroom reached reached by by the the modern modern corridor corridor was was the the large large sepulchral sepulchral cell cell reservedreserved for for members members of of the the Confraternity Confraternity of of the thethe Lizza, Lizza,Lizza, previously previouslypreviously positioned positionedpositioned under underunder the thethe Congrega’sCongrega’s house house (Figure (Figure6 ,6, X). X). It It is is a a rectangular rectangular room room (8.10 (8.10× ×4.00 4.00 m)m) characterized characterized by by a a depresseddepressed barrel barrel vault vault with with an an east-west east-west axis, axis, whose whose modern modern plastering plastering no no longer longer allows allows tototo understand understandunderstand where wherewhere the thethe trap traptrap door doordoor was waswas placed: placedplaced:: the thethe slightly slightlyslightly oblique obliqueobliqueprofile profileprofile of ofof the thethe western westernwestern sideside would would tend tend to to outline outline the the layout layout of of the the back back wall wall of of the the same same Congrega’s Congrega’s house. house. TheThe lastlast andand largestlargest room has has a a rectangular rectangular north-south north-south oriented oriented plan plan (10.00 (10.00 × 4.90× 4.90 m) and m) anda depressed a depressed barrel barrel vault reinforced vault reinforced by two arches by two 50 arches cm wide 50 in cm the wide middle in part the middle(Figure 6, part XI). (TheFigure longitudinal6, XI). The axis longitudinal is parallel axis to the is parallel wester ton side the westernof the Congrega’s side of the sepulchral Congrega’s cell sepul- and chralitit isis likelylikely cell and thatthat it isthethe likely houseshouses that onceonce the housescloseclose toto once ththe pronaos close to the had pronaos the same had alignment, the same alignment,in order to innot order unload to notthe unloadweight theon the weight vault on (Figure the vault 11b). (Figure The memoirs 11b). The describe memoirs this describeunderground this undergroundplace as cool placeand dry as cool and andused dry for and the used storage for theof grain storage and of other grain provisions and other provisionsneeded by neededthethe religiousreligious by the duringduring religious theirtheir during summersummer their holidaysholidays summer inin holidays Alezio.Alezio. in Alezio.

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Finally, a staircase with a U-path goes from the southern side of room XI up to the externalFinally, churchyard a staircase near the with southern a U-path side goes of fromthe high the southernpronaos. side of room XI up to the external churchyard near the southern side of the high pronaos. 3.2. GPR 3.2. GPR Figure 13 shows two processed radar sections related to Area 1. Four significant Figure 13 shows two processed radar sections related to Area 1. Four significant anomalies, labelled D, F, M and D are clearly visible. The anomaly F, inside the dashed anomalies, labelled D, F, M and D are clearly visible. The anomaly F, inside the dashed yellow box, has a typical shape of small hyperbolas probably due to the presence of a yellow box, has a typical shape of small hyperbolas probably due to the presence of a metal metal reinforcement (electro-welded mesh) of the paving; the anomalies M at a depth be- reinforcement (electro-welded mesh) of the paving; the anomalies m at a depth between tween 0.5 m and 1.0 m are probably related to the presence of walls; anomaly T at a depth 0.5 m and 1.0 m are probably related to the presence of walls; anomaly T at a depth between between0.2 m and0.2 m 0.3 and m is 0.3 probably m is probably related related to the presence to the presence of pipes. of pipes.

Figure 13. The GPR processed radar sections related to the Area 1; D: partial collapse event; F: metal Figure 13. The GPR processed radar sections related to the Area 1; D: partial collapse event; F: reinforcement; M: walls; T: pipes. metal reinforcement; M: walls; T: pipes. A partial collapse event is indicated with D. This event could have been due to the presenceA partial of smallcollapse voids event possibly is indicated caused with by rainy D. This events event and could probably have aggravated been due byto the presencepassage of of small heavy voids vehicles. possibly caused by rainy events and probably aggravated by the passageFigure of heavy 14 showsvehicles. two processed radar sections related to Area 2. Four significant anomalies,Figure 14 labelled shows two A1, A2,processed A3 and radar A4 are sectio clearlyns related visible. to The Area anomalies 2. Four A1significant and A2, anomalies,at depth betweenlabelled 0.5A1, m A2, and A3 1.0 and m, are A4 probably are clearly related visible. to the The presence anomalies of the alreadyA1 and knownA2, at depthparts between of the underground 0.5 m and 1.0 rooms m, are II, probably III, VI and related VIII (see to the above presence paragraph of the 3); already the anomalies known partsA3 of and the A4, underground at depth between rooms 0.8 II, m III, and VI 2.5 an md VIII are probably(see above related paragraph to the presence3); the anomalies of one or A3two and unknown A4, at depth underground between 0.8 rooms m and located 2.5 m west are ofprobably room VI. related to the presence of one or two unknownFigure 15 showsunderground two processed rooms located radar sections west of relatedroom VI. to Area 3. An interesting re- flected event is highlighted (labelled A) at a depth between 0.5 m and 0.7 m. This event could be due to the presence of an empty underground room, which was subsequently filled. Figure 16 shows two processed radar sections related to Area 4. Here the reflected events at a depth between 0.5 m and 1.0 m (indicated with A5 and A6) are visible. They are probably relating to the presence of the already known parts of the underground rooms IX and X (see Section3 above).

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Figure 14. The GPR processed radar sections related to the Area 2; A1 and A2: known parts of the underground rooms; A3 and A4: unknown underground rooms.

Figure 15 shows two processed radar sections related to Area 3. An interesting re- flected event is highlighted (labelled A) at a depth between 0.5 m and 0.7 m. This event Figure 14. The GPR processed radar sections related to the Area 2; A1 and A2: known parts of the Figurecould 14.be Thedue GPR to the processed presence radar of sectionsan empt relatedy underground to the Area room, 2; A1 andwhich A2: knownwas subsequently parts of the underground rooms; A3 and A4: unknown underground rooms. undergroundfilled. rooms; A3 and A4: unknown underground rooms. Figure 15 shows two processed radar sections related to Area 3. An interesting re- flected event is highlighted (labelled A) at a depth between 0.5 m and 0.7 m. This event could be due to the presence of an empty underground room, which was subsequently filled.

FigureFigure 15.15.The The GPRGPR processedprocessed radarradar sectionssections relatedrelated toto the the Area Area 3; 3; A: A: empty empty underground underground room. room.

FigureFigure 17 16 shows shows two two processed processed radar radar sections sections related related to to Area Area 6. Here4. Here some the reflectedreflected events,events indicatedat a depth by between F within 0.5 the m dashed and 1.0 yellow m (indicated box, are with related A5 toand the A6) presence are visible. of a metal They reinforcementare probably (electro-weldedrelating to the mesh)presence of theof paving;the already other known reflected parts events of atthe depth underground between Figure 15. The GPR processed radar sections related to the Area 3; A: empty underground room. 0.7rooms m and IX and 1.1 m X (labelled(see Section A9) 3 probably above). related to the presence of the northern part of the alreadyFigure known 16 cryptshows XI two (see processed above paragraph radar sections 2). related to Area 4. Here the reflected In the very small Area 5 no significant results were found. events at a depth between 0.5 m and 1.0 m (indicated with A5 and A6) are visible. They The time slices were built using a time interval ∆t = 5 ns that correspond to a thickness are probably relating to the presence of the already known parts of the underground of 27.5 cm. One approach for visualizing 3D is the use of iso-surface rendering, assembled rooms IX and X (see Section 3 above). from all processed radargrams [18–20,27,28]. Figure 18 shows the most significant time slices superimposed on the plan of the areas investigated. The time slices show the normalized amplitude using a range defined by blue as zero and red as 1.

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Figure 16. The GPR processed radar sections related to the Area 4; A5 and A6: known under- ground rooms.

Figure 17 shows two processed radar sections related to Area 6. Here some reflected events, indicated by F within the dashed yellow box, are related to the presence of a metal reinforcement (electro-welded mesh) of the paving; other reflected events at depth be- FigureFigure 16.16. TheThe GPR GPR processed processed radar radar sections sections related related to tothe the Area Area 4; A5 4; and A5 andA6: known A6: known under- under- tweenground 0.7 rooms. m and 1.1 m (labelled A9) probably related to the presence of the northern part groundof the already rooms. known crypt XI (see above paragraph 2). Figure 17 shows two processed radar sections related to Area 6. Here some reflected events, indicated by F within the dashed yellow box, are related to the presence of a metal reinforcement (electro-welded mesh) of the paving; other reflected events at depth be- tween 0.7 m and 1.1 m (labelled A9) probably related to the presence of the northern part of the already known crypt XI (see above paragraph 2).

FigureFigure 17.17. TheThe GPR GPR processed processed radar radar sections sections related related to tothe the Area Area 6; F: 6; metal F: metal reinforcement; reinforcement; A9: A9: knownknown crypt.crypt.

InIn the the time very slices small ranging Area 5 fromno significant 0.7 m to 0.9 results m depth were related found. to the Area 1 (Figure 18), rel- ativelyThe high-amplitude time slices were alignments built using (labelled a time interval M, respectively) Δt = 5 ns that are clearlycorrespond visible. to a These thickness cor- of 27.5 cm. One approach for visualizing 3D is the use of iso-surface rendering, assembled respondFigure 17. to The the GPR anomalies processed labelled radar sections m in the related radargrams to the Area (Figure 6; F: metal 13). Thesereinforcement; anomalies A9: are relatedknownfrom all crypt. to processed the walls radargrams relative to the[18–20,27,28]. old structure of the church demolished in 1959–1961 (specifically the northern nave). Another anomaly, labelled C, is visible in the same time slice.In This the anomalyvery small is Area related 5 no to significant the well-known results entrance were found. corridor to the underground system of crypts. The time slices were built using a time interval Δt = 5 ns that correspond to a thickness of 27.5In thecm. timeOne sliceapproach related for to vi thesualizing Area 2 (Figure3D is the 18 use) ranging of iso-surface from 0.8 rendering, m to 1.0 m assembled depth the anomaliesfrom all processed labelled A3 radargrams and A4 are [18–20,27,28]. well evidenced. They are related to the unknown develop

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of the system of crypts below the surface of the church. Specifically, they could be related to oneFigure or two 18 unknown shows the underground most significant rooms time located slices westsuperimposed of the room on VI the documented plan of the byar- theeas laserinvestigated. scanner surveyThe time (Figure slices8 show). In the the easternmost normalized partamplitude of this using Area 2, a somerange anomaliesdefined by couldblue as be zero also and linked red toas the1. demolished structures of the old sacristy.

FigureFigure 18.18. TheThe GPRGPR timetime slices:slices: AreaArea 11 (0.7–0.9(0.7–0.9 mm depth); depth); Area Area 2 2 (0.8–1.0 (0.8–1.0 m m depth); depth); Area Area 3 3 (0.4–0.5 (0.4–0.5 m depth);m depth); Area Area 4 (0.8–0.9 4 (0.8–0.9 m depth);m depth); Area Area 6 (0.5–0.7 6 (0.5–0.7 m depth).m depth).

InIn thethe timetime sliceslices related ranging to from the Area 0.7 m 3 to (Figure 0.9 m 18 depth), ranging related from to the 0.4 Area m to 1 0.5 (Figure m depth, 18), therelatively anomaly high-amplitude labelled A evidences alignments the presence(labelled ofM, an respectively) unknown filled are clearly cavity locatedvisible. underThese thecorrespond paving of to the the pronaos. anomalies labelled M in the radargrams (Figure 13). These anomalies are relatedIn the timeto the slice walls related relative to theto the Area old 4 structure (Figure 18 of), the ranging church from demolished 0.8 m to 0.9in 1959–1961 m depth, the(specifically anomalies the A5, northern A6 and nave). A7 confirm Another the anomaly, well-known labelled sector C, is of visible the system in the same of crypts; time specifically,slice. This anomaly the anomalies is related A5 andto the A6 well- correspondknown toentrance the rooms corridor IX and to X,the while underground anomaly A7system is related of crypts. to the well-known corridor that connects these rooms to the other crypts. Furthermore,In the time the slice anomaly related labelled to the Area C is visible 2 (Figure in the 18) same ranging time from slice 0.8 and m Ito related 1.0 m todepth the southernthe anomalies wall oflabelled the demolished A3 and A4 Congrega’s are well ev house.idenced. They are related to the unknown developLastly, of the in the system time sliceof crypts related below to the the Area surface 6 (Figure of the 18 church.), ranging Specifically, from 0.5 mthey to 0.7could m depth,be related the anomalyto one or A9two confirm unknown the underground well-known northern rooms located part of west the crypt of the XI. room VI doc- umented by the laser scanner survey (Figure 8). In the easternmost part of this Area 2, 4. Discussion some anomalies could be also linked to the demolished structures of the old sacristy. InIn orderthe time to slice improve related the to interpretation the Area 3 (Fig ofure geophysical 18), ranging anomalies, from 0.4 m GPR to 0.5 data m depth, were integratedthe anomaly with labelled the 2D A andevidences 3D models the presence produced of an by unknown laser scanner filled survey. cavity located In particular, under GPRthe paving time slices of the and pronaos. profiles were georeferenced in the map of the church. First of all, the GPRIn the data time interpretation slice related to was the favouredArea 4 (Fig byure the 18), iso-amplitude ranging from surface 0.8 m to visualization 0.9 m depth, (Figurethe anomalies 19). The A5, GPR A6 resultsand A7 highlighted confirm the awell-k seriesnown of anomalies sector of regardingthe system various of crypts; buried spe- archaeologicalcifically, the anomalies structures. A5 Among and A6 the correspond anomalies to evidenced the rooms in IX the and area X, 1while canbe anomaly identified A7 asis therelated remains to the of well-known the old built corridor structure that of the connects church these (Figure rooms 13, M). to Otherthe other anomalies crypts. withFur- highthermore, amplitude the anomaly are due tolabelled the presence C is visible of unknown in the buriedsame time rooms slice (Figure and 14I related, A3 and to A4). the Insouthern the other wall investigated of the demolished areas numerous Congrega’s anomalies house. corresponding to known buried rooms. Particularly in the area 3 (Figure 15, A) a filled buried room was found. Traces of this room Lastly, in the time slice related to the Area 6 (Figure 18), ranging from 0.5 m to 0.7 m had been lost. At this point is important to integrate the GPR data with the laser scanner depth, the anomaly A9 confirm the well-known northern part of the crypt XI. data. This step is fundamental to place the structures into a three-dimensional framework. 4. Discussion In order to improve the interpretation of geophysical anomalies, GPR data were in- tegrated with the 2D and 3D models produced by laser scanner survey. In particular, GPR

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timetime slicesslices andand profilesprofiles werewere georeferencedgeoreferenced inin thethe mapmap ofof thethe church.church. FirstFirst ofof all,all, thethe GPRGPR datadata interpretationinterpretation waswas favouredfavoured byby thethe iso-amplitudeiso-amplitude surfacesurface visualizationvisualization (Figure(Figure 19).19). TheThe GPRGPR resultsresults highlightedhighlighted aa seriesseries ofof anomalanomaliesies regardingregarding variousvarious buburiedried archaeologicalarchaeological structures.structures. AmongAmong thethe anomaliesanomalies evidencedevidenced inin ththee areaarea 11 cancan bebe identifiedidentified asas thethe remainsremains ofof thethe oldold builtbuilt structurestructure ofof thethe churchchurch (Fig(Figureure 13,13, M).M). OtherOther anomaliesanomalies withwith highhigh ampli-ampli- tudetude areare duedue toto thethe presencepresence ofof unknownunknown buriedburied roomsrooms (Figure(Figure 14,14, A3A3 andand A4).A4). InIn thethe otherother investigatedinvestigated areasareas numerousnumerous anomaliesanomalies correspondingcorresponding toto knownknown buriedburied rooms.rooms. Par-Par- ticularly in the area 3 (Figure 15, A) a filled buried room was found. Traces of this room Sensors 2021, 21, 2205 ticularly in the area 3 (Figure 15, A) a filled buried room was found. Traces of this15 room of 17 hadhad beenbeen lost.lost. AtAt thisthis pointpoint isis importantimportant toto integrateintegrate thethe GPRGPR datadata withwith thethe laserlaser scannerscanner data.data. ThisThis stepstep isis fundamentalfundamental toto placeplace thethe ststructuresructures intointo aa three-dimensionalthree-dimensional framework.framework.

Figure 19. The GPR iso-surfaces: (a) Area 1; (b) Area 2. FigureFigure 19.19. TheThe GPRGPR iso-surfaces:iso-surfaces: ((aa)) AreaArea 1;1; ((bb)) AreaArea 2.2.

TheThe createdcreated iso-surfacesiso-surfacesiso-surfaces volumevolume (Figures(Figures 1919 andandand 2020)20)) waswaswas exportedexportedexported ininin aaa 3D3D3D asciiasciiascii filesfilesfiles ininin orderorderorder tototo bebebe mergedmergedmerged withwithwith thethethe polygonalpolygonalpolygonal surfacessusurfacesrfaces obtainedobtained withwith thethe laserlaser scannerscanner data.data. HereHere is isis possible possiblepossible to toto insert insertinsert the thethe GPR GPRGPR iso-surfaces iso-surfacesiso-surfaces volume volumevolume at the atat thethe exact exactexact depth. depth.depth. In this InIn this waythis wayway a sort aa ofsortsort virtual ofof virtualvirtual excavation excavationexcavation is obtained isis obtainedobtained in which inin whwh theichich georadar thethe georadargeoradar anomalies anomaliesanomalies are positioned areare positionedpositioned in the inin exactthethe exactexact spatial spatialspatial position positionposition (Figure (Figure(Figure 21a,b) 21a,b)21a,b) and allow andand allowallow to compare toto comparecompare the known thethe knownknown structures structuresstructures with those withwith detectedthosethose detecteddetected by the byby geophysical thethe geophysicalgeophysical data allowing datadata allowiallowi to getngng a toto relationship getget aa relationshiprelationship between betweenbetween the visible thethe and visiblevisible the notandand visible. thethe notnot visible.visible.

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FigureFigure 20.20. TheThe GPRGPR iso-surfaces:iso-surfaces: ((aa)) AreaArea 3;3; (((bb)) AreaAreaArea 4;4;4; (((ccc))) AreaAreaArea 6.6.6.

FigureFigure 21.21.The The 3D3D representationrepresentation ofof thethe underground underground anomalies anomalies in in the the Areas Areas 1 1 ( a(a)) and and 4 4 ( b(b).).

5.5. ConclusionsConclusions ThanksThanks toto thethe integrationintegration withwith laserlaser scannerscanner data,data, GPRGPR surveysurvey offeredoffered newnew datadata onon thethe extensionextension ofof undergroundunderground rooms rooms and and buried buried walls. walls. InIn particular,particular, the the laser laser scanner scanner survey survey has has allowed allowed for for the the production production of of the the complete complete mapmap ofof thethe knownknown crypts.crypts. InIn thisthis newnew planplan itit waswas possiblepossible toto distinguishdistinguish thethe exactexact positionposition inin spacespace (shape(shape andand depth)depth) of of the the various various crypts. crypts. TheThe geophysicalgeophysical prospectingprospecting allowed allowed us us toto highlighthighlight numerousnumerous anomalies, anomalies, many many of of them them of of archaeologicalarchaeological interest, interest, in in part part related related to the known crypts (rooms II-XI) and ancient structures demolished in 1959–1961 (such as the northern nave and the Congrega’s house), and in part linked to new underground rooms or cavities (such as anomalies A, A3 and A4, in the nave of the church and in the pronaos), previously unknown and yet to be explored. The integration with the laser scanner data allowed us to validate the results of GPR survey. Indeed, it was possible to compare the events reflected of the electromagnetic waves on known underground structures with those of unknown buried structures on the radar section and allow their interpretation. Moreover, the georeferenced time slices allow the identification of the exact position of the unknown buried rooms. The 3D iso-surfaces in- serted into the virtual environments facilitate the interpretation phase and allowed us to increase the knowledge of the studied monument evidencing its past and present structure organization. The results will also be useful for the planning of future targeted excavations.

Author Contributions: Methodology, L.D.G., F.G., I.F. and G.L.; software, L.D.G., F.G., I.F. and G.L.; validation, L.D.G., F.G., I.F., G.L. and G.S.; formal analysis, G.L. and G.S.; investigation, L.D.G., F.G., I.F. and G.L.; data curation, L.D.G., F.G., I.F. and G.L.; writing-original draft preparation, F.G., I.F. and G.L.; writing-review and editing, G.L. and G.S.; supervision, G.S. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on request from the corresponding author. Acknowledgments: We thank the Superintendence of Archeology, Fine Arts and Landscape for the provinces of Brindisi, Lecce and Taranto, the Diocese of Nardò-Gallipoli for granting all the neces- sary authorizations for carrying out the research activities and the Municipality of Alezio for the support given to the operations on site. Conflicts of Interest: The authors declare no conflict of interest.

References 1. Ferrari, I.; Scardozzi, G. Contributo alla Carta Archeologica di Alezio; Scirocco Editore: Bari, Italy, 2016.

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to the known crypts (rooms II-XI) and ancient structures demolished in 1959–1961 (such as the northern nave and the Congrega’s house), and in part linked to new underground rooms or cavities (such as anomalies A, A3 and A4, in the nave of the church and in the pronaos), previously unknown and yet to be explored. The integration with the laser scanner data allowed us to validate the results of GPR survey. Indeed, it was possible to compare the events reflected of the electromagnetic waves on known underground structures with those of unknown buried structures on the radar section and allow their interpretation. Moreover, the georeferenced time slices allow the identification of the exact position of the unknown buried rooms. The 3D iso-surfaces inserted into the virtual environments facilitate the interpretation phase and allowed us to increase the knowledge of the studied monument evidencing its past and present structure organization. The results will also be useful for the planning of future targeted excavations.

Author Contributions: Methodology, L.D.G., F.G., I.F. and G.L.; software, L.D.G., F.G., I.F. and G.L.; validation, L.D.G., F.G., I.F., G.L. and G.S.; formal analysis, G.L. and G.S.; investigation, L.D.G., F.G., I.F. and G.L.; data curation, L.D.G., F.G., I.F. and G.L.; writing-original draft preparation, F.G., I.F. and G.L.; writing-review and editing, G.L. and G.S.; supervision, G.S. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on request from the corresponding author. Acknowledgments: We thank the Superintendence of Archeology, Fine Arts and Landscape for the provinces of Brindisi, Lecce and Taranto, the Diocese of Nardò-Gallipoli for granting all the necessary authorizations for carrying out the research activities and the Municipality of Alezio for the support given to the operations on site. Conflicts of Interest: The authors declare no conflict of interest.

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