Conservation of the Modern Rampart Defensive Walls - the Experience of the City of Padua

Conservation of the modern rampart defensive walls - the experience of the City of Padua

C. Modena% G. Carbonara^ & M. Berti^ * Department of Construction and Transport, Faculty of Engineering,

University of Padua, Via Marzolo 9, Padova, Italy Email: modena@caronte. die. unipd. it

2 Department of History and Restoration of the Architecture, Faculty of Architecture, University "La Sapienza", Via Monte Zebio 32, Rome, Italy

Email: restauro@axrma. uniromal. it 3 Public Works Department of the Municipality of Padua, Bureau for the

Conservation of Walls, Via VIII Febbraio, Padova, Italy Email: mauriberti@tin. it

Abstract

The technological and constructive solutions adopted to build defensive walls around the towns had to be substantially updated during the sixteenth century in order to efficiently counteract the devastating effects of the more and more powerful artillery used by attacking armies. The defensive works, in particular, became very complex systems made of sophisticated masonry structures (walls, vaults, tunnels) and massive earthworks. In this paper, typical aspects of their structural conservation are discussed based on the analysis of the original constructive solutions, their evolution and their current situation. The presentation is based on the design experiences and the studies conducted by the authors during recent restoration interventions carried out on the defensive works built around Padua in the sixteenth century are presented.

1 Introduction

For the past fifteen years the Padova City Council has been continuously involved in conserving the walls of the city which had been neglected over the preceding decades. The rampart system of Padua extends for about eleven kilometres

656 Structural Studies, Repairs and Maintenance of Historical Buildings

(Figure 1). One of the most noteworthy results of these last years is the establishment of a methodology of intervention based on scheduled maintenance which makes it possible for the local administration to adequately conserve and care for this ancient and complex structure of great dimensions, with it own resources. This method requires limited resources, but allows degradation to be reduced drastically with a minimal annual maintenance programme and at the same time allows single restoration projects to be carried out, or postponed, according to a classification of urgency.

31 Bastione Bastione Moro Comune di Padova M( AREA EDILIZIA PUBBLICA SETTORE EDILIZIA MONUMENTALE UFFICIO MURA

6 Castelnuovo

ind*ortelloVecchio

Bastione Comaro

Pontecorvo SISTEMA BASTIONATO CINQUECENTESCO DI PADOVA Bastione S. Giustina Programmazione degli interventi di 17 manutenzione e di restauro Bastione Suddivisione in 33 tratti principali con S. Croce ripartizioni di secondo livello * Alicomo

Figure 1: Schematic plant of the walls and ramparts of Padua.

The studies, projects and restoration carried out up to now have indicated that priority should be given to some structural interventions. Conservation of the exposed masonry surfaces depends in fact on the entire fabric of the construction that includes building materials such as bricks, stones and, above all earth. The earthwork has undergone consolidation, erosion and transformations over time that have caused inevitable interactions with the walled structures against which

Structural Studies, Repairs and Maintenance of Historical Buildings 657

they are built. The authors' experience regarding the conservation of some of the ramparts 1^,3,4,5,6 ;% briefly described in the following.

2 Historical background

From an investigation of the abundant 16^ century literature^9,10,11,12 ^ emerges that military engineering developed mainly along the lines of defence systems, while for a long time offensive systems remained unchanged in both technology and effectiveness. One of the principal concerns of military engineers, having a good knowledge of both defensive and offensive techniques, was to improve the wall's capacity to absorb artillery fire. The treatiser who can probably best illustrate the theories and ideas of planners and builders of the evolved rampart system, was Giacomo Lanteri da

Paratico^. Lanteri, who published a treatise on earth fortifications in Venice in 1559, wrote an entire chapter on the structural interaction between masonry and earth: Che ordine si dee tenere havendo da fare un riparo a canto a qualche muro. (The rules to be followed when building a shelter next to a wall.) He observed the precarious nature of a wall built against an earthwork. The main problem is obviously the action exerted by the earth against the wall, which manifests itself and evolves over time in a complex manner, and depends on many parameters, such as environmental conditions, the consolidation process and subsidence of the wall-earth system. This action had to be resisted. He suggested the earthwork be detached from the wall by the distance of at least a palm and that the construction be carried out in layers reinforced with wood positioned vertically and horizontally, with the aim of reducing vertical deformation. Lanteri prescribed the inclination of the earthwork scarp as one foot in every six of height while the inclination of the masonry had the ratio of one to five. In the superimposition of the two profiles the greater inclination of the light brick cladding would leave space below, at the enlargement of the earthwork web. Sections of wall corresponding to this prescription can be observed in Lucca, Jesi and Ferrara, for example, and are at the very height of technical and formal maturity in cladding earthworks. The earth is settled in its optimal form and the cladding in brick regulates and generally protects against meteorological elements. During the Cambrai war, the Padua defence system was laid out very fast^ and the shelters and earth ramparts were probably built without the structural solutions that Lanteri set up later. Concerning this point, Promis^ wrote succinctly: "The city was reclaimed by the Venetians on 17 July of the year 1509. The allies of Cambrai made camp on the first days of September; the Venetians therefore had but a month and a half to carry out the never-ending building of the defences that were deemed necessary". In some accounts of how the fortifications resisted the first assaults, Raffaello Brenzoni^ and Giuseppe Fiocco saw an unequivocal early sign that the earth rampart was to be re-shaped as a pentagonal bulwark built with substantial brick material, in the same way that Michele

658 Structural Studies, Repairs and Maintenance of Historical Buildings

Sanmicheli also did. The information was too elusive. In Padua, during the years of the definitive shaping of the wall, there was a presence of engineers and commanders who were knowledgeable of, or had participated in, the constructive conception of prevalently masonry defences; at least all those who came from the Military Schools of central Italy. It is believed that for logistic reasons and economy of construction, much of the primitive earth defences had to be conserved. Probably some sectors of the wall were not even appropriate to earthworks. This is the case of the fortress that conserves all the building and architectural properties found in the Tramontano castle of Potenza, namely pre-modern systems of defence. However, only systematic investigation of archives by historians and an interpretation of documents brought to light will enable us to establish which sections of the Padua wall were clad with brickwork after a complete and efficient solution with the use of earth alone.

3 The "Santa Croce" ramparts

In setting up a conservation methodology appropriate to the type of structure outlined briefly above, two particular elements have been observed in the ramparts of Santa Croce: the parapet and buttresses. At the start of the study, the area was still called la montagnola (the hillock) because of the thick vegetation that covered the entire rampart. The year inscribed on the south-west side - 1548 - can be considered a certain historical date. The attribution of the monument to Michele Sanmicheli by some historians, and two well-known detailed 19* century maps, whose details correspond, initially suggested that restoration of the architecture to its "original state" was certainly possible. As field studies and investigations went on, the idea of being able to reach what had always been thought of as the "original state" became more and more improbable. It had already become very difficult to think of restoration as being limited to just managing the spontaneous vegetation and reducing the structure to an acceptable state of safety.

3.1 The parapet

Among the first tasks faced in the material identification of the ramparts was deforestation of the thick vegetation growing in the deep layer of earth at the summit. Initially only the vegetation whose root system was definitely interfering with the masonry structure of the front under the layer of earth was removed. The presence of guard trenches at the edge of the front and sides of the rampart, as well as traces of two garrets of which there is mention in the 19* century survey by Ronzani^ , led us to consider at length the formal and functional characteristics of what appeared to be an evident transformation. It was then decided to totally eliminate the vegetation, whose root system was undermining the wall at many points. It was then necessary to define a possible profile of the parapet and the high stronghold, with or without earth, that could be appropriate for the future conservation of the monument (Figure 2).

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Figure 2: View of S. Croce rampart.

For various reasons it was not possible to draw much useful data about this subject from the abundant research carried out on archival and printed sources. A decision was taken, however, to apply a uniform plaster coating in place of the previous layer of earth on the front and side parapets of the south-east face. However, many questions remain unanswered regarding this question; whether the layer of earth on top of a bare parapet without herring-bone paving is an appropriate solution for defensive systems in the second half of the 16"' century.

Figure 3: Earthflll on S. Croce rampart.

660 Structural Studies, Repairs and Maintenance of Historical Buildings

In the Santa Croce rampart the vertical portion of wall above the cordon was not knocked down making it oblique, but the conformation of the inclined upper level of the parapet would have been adequate. Without the herring-bone cladding in brick it would have been covered by a thick layer of earth to absorb enemy artillery hits. This solution was commonly proposed by 16^ century military engineers (Figure 3). Perhaps a similar case of reduced transformation of the upper part of the rampart can be observed in Bernardo Bellotto's view of the city of Dresden (c. 1750).

3.2 Front and side buttresses

Girolamo Maggi, in his treatise on fortifications, refers to buttresses and mentions Vitruvio, San Marino, Tartaglia, Capitan Frate da Modena and Leon

Battista Albert!. "Albert! prescribed arches to be built between one buttress and the next, or vaults as we wish to call them, and that the spaces be filled with clay mixed with hay"..."M. Michel San Michele Veronese prescribed the vaults to be buttressed so that they come up to the level of the stronghold above them,and to build the adjoining parapet joined to those in brick to a total (width) of 18 feet so that a corridor (the bank) of 10 feet remains". In the Santa Croce rampart three buttress arches between one side and the adjoining face have been partially explored by freeing them of the earthwork (Figure 4).

Figure 4. Arch buttresses of S. Croce rampart.

Structural Studies, Repairs and Maintenance of Historical Buildings 661

The construction turns out to be very similar to that of Sanmicheli as quoted by Maggi, including the peculiarity of the areas splayed towards the interior favouring containment of the earth. Any restoration work here cannot ignore the previous question of the parapet which has been altered in respect to its original state. This transformation could have taken place at the end of the 16^ century or at a time close to the 19^ century (Figure 4). Regarding the interaction between earth and walled structures, the important role of the connecting vaults between the buttresses becomes clear. More than four hundred years after construction of the ramparts, as Lanteri foresaw in his earth defences, the earthwork up against the masonry of the sides has subsided, because of natural packing, to the proportion of at least one tenth of the height of the earthwork itself. The vaults built on earth (obviously well before the current state of earth consolidation is reached) have therefore had to support totally the parapet and all loads (including those caused by manoeuvring and cannon fire) applied to it. Therefore we are not only dealing with elements of "enclosure" and

"confinement" of the earthwork but of sturdy structures that have successfully carried out important static functions.

Figure 5: Deterioration of the masonry vaults of Moro II e S. Croce ramparts.

The stability and transformation of the parapet causes concern; without its herring-bone brick cladding, and covered with earth, which is not sufficiently waterproof, a process of disintegration of the masonry structure is underway. Some bricks have already fallen, detaching from the intrados. Unfortunately this can cause, although rarely, vaulting to collapse, as the field of restoration has taught us (Figure 5).

662 Structural Studies, Repairs and Maintenance of Historical Buildings

4 The "San Prosdocimo", "MoroII" and "Moro I" ramparts

The phenomena found in the ramparts of Santa Croce are visible from the public road as is also the case for the Moro II ramparts (1530-1532). The structure of the San Prosdocimo (1528?) and Moro I (1530-1532) ramparts is more complex and is currently being studied by the authors. The ramparts of San Prosdocimo were deliberately damaged by the

French occupation in 1801. Explosives had a great effect, succeeding in breaching the walls which are up to 5 metres thick.

Figure 6: Damages and investigations on S. Prosdocimo rampart.

The authors have carried out a careful survey and some core samples of the foundations to draw up a consolidation project which conserves most of the deformations of the structure, but permits the public to visit the underground areas in safety. As for the ramparts of San Prosdocimo, a survey aimed at the state of the structure in particular will be carried out on the Moro I ramparts which were hit by

German bombs during World War II, in 1944. The nature of some this damage leads us to think of a previous explosion which may have occurred, as in the case of the San Prosdocimo ramparts, because of the explosion of ammunition inside the rampart.

In such cases the main structural problem actually is (as can be seen in the sections of Fig. 7) to avoid local collapses due to lack of masonry continuity and to the material deterioration phenomena which have been previously cited. Schematic indications of how the interventions are intended to be carried on S.

Prosdocimo rampart out are given in Fig. 7b, based on accurate surveys and records of the existing situation (Figure 7a). The idea is to use masonry reconstruction to make the site safe and friendly to the visitors, whilst respecting the conservation criteria of using compatible (from both the physical, chemical, mechanical and aesthetic points of view) and removable materials.

Fig. 7a, b: Proposals for the consolidation of S. Prosdocimo rampart.

664 Structural Studies, Repairs and Maintenance of Historical Buildings

References

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antica e tecnologia moderna, Padova 1989, pp. 15-18.

2. M. BERTI, L'intonacatura delle murature nei sistemi bastionati cinquecenteschi, in "Scienze e Beni Cultural*", Padova 1990, pp. 127-137.

3. M. BERTI, Conservazione dei sistemi bastionati cinquecenteschi. Conservazione delle loro superfici in laterizio. Esperienze della citta di Padova, in "Scienza e Beni Culturali", Padova 1992, pp. 677-689.

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10. M. G. LANTERI, Del modo difare iforti di terra, Venezia 1559.

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12. H. CATANEO, Dell'arte militare: Libri cinque, ne' quali si tratta il modo di fortificare, offendere, et difendere unafortezza^ Brescia 1608.

13. G. BRESCIANI ALVAREZ, Gli interventi cinquecenteschi nella cinta muraria di Padova, in L 'architettura militare veneta del Cinquecento, Vicenza 1980.

14. C. PROMIS, Martini Francesco di Giorgio. Trattato di architettura civile e militare, Torino 1841.

15. R. BRENZONI, Fra Giovanni Giocondo Veronese, Firenze 1940.

16. F. RONZANI-G. LUCIOLLI, Lefabbriche di Michele Sanmicheli, Venezia 1831.