Deadly CO2 Gases in the Plutonium of Hierapolis (Denizli, Turkey)

Archaeological and Anthropological Sciences (2019) 11:1359–1371 https://doi.org/10.1007/s12520-018-0599-5

ORIGINAL PAPER

Deadly CO2 gases in the Plutonium of Hierapolis (Denizli, Turkey)

Hardy Pfanz1 & Galip Yüce2 & Ahmet H. Gulbay3 & Ali Gokgoz4

Received: 30 March 2016 /Accepted: 16 January 2018 /Published online: 12 February 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018

Abstract Using a portable gas analyzer system, the geogenic gas regime below and around an ancient gate to hell at Hierapolis/Phrygia was characterized. The site was first described by Strabo and Plinius as a gate to the underworld. During centuries, it attracted even ancient tourists. In a grotto below the temple of Pluto, CO2 was found to be at deadly concentrations of up to 91%. Astonishingly, these vapors are still emitted in concentrations that nowadays kill insects, birds, and mammals. The concentrations of CO2 escaping from the mouth of the grotto to the outside atmosphere are still in the range of 4–53% CO2 depending on the height above ground level. They reach concentrations during the night that would easily kill even a human being within a minute. These emissions are thought to reflect the Hadean breath and/or the breath of the hellhound Kerberos guarding the entrance to hell. The origin of the geogenic CO2 is the still active seismic structure that crosses the old town of ancient Hierapolis as part of the Babadag fracture zone. Our measurements confirm the presence of geogenic CO2 in concentrations that explain ancient stories of killed bulls, rams, and songbirds during religious ceremonies. They also strongly corroborate that at least in the case of Hierapolis, ancient writers like Strabo or Plinius described a mystic phenomenon very exactly without much exaggeration. Two thousand years ago, only supernatural forces could explain these phenomena from Hadean depths whereas nowadays, modern techniques hint to the well-known phenomenon of geogenic CO2 degassing having mantle components with relatively higher helium and radon concentrations.

Keywords Carbon dioxide . Helium . Radon . Charonion . Gate tohell . Geogenic gases . Hades . Mephiticexhalations . Mofette

Introduction town, probably a Seleucid foundation in the second century B.C. (Gerster 2005 p. 162; Porter 2016 p. 355), developed The Pamukkale thermal province located in the east of the during the Roman Empire and was already famous in Buyuk Menderes Graben is famous for its thermal springs Byzantine times (Ring et al. 1995 p. 327; Rigsby 1996; and snow-white travertine formations and also for the excava- Cohen 2006; Zwingmann 2012; Nyquist 2014; Şimşek and tions of ancient Hierapolis. First recordings of the old city of D’Andrea 2017). In this period, a huge pilgrim sanctuary was Hierapolis were made by Strabo (XII, 8, 17) and also Plinius built around the tomb of the Apostle Philip (D’Andria 2003). the Elder (Nat. Hist. V, 105) mentions this famous town. The Geologically, the holy town Hierapolis is cut longitudinally by several parallel fractures of the Pamukkale fault (intra-plate tectonics) as the part of extensional straining of the western * Hardy Pfanz Anatolian extensional regime or the west Anatolian horst- [email protected] graben system extending from the Aegean Sea to central Anatolia (Seyitoglu and Scott 1996; Kaymakci 2006). It is 1 Institute of Applied Botany and Volcano Biology, University of specified mainly by major horsts and grabens at E–W trending, Duisburg-Essen, 45117 Essen, Germany and NW–SE to NE–SW oriented relatively short and locally 2 Department of Geological Engineering, Hacettepe University, suspended cross-grabens (Bozkurt 2003). Thus, Hierapolis is Beytepe, 06800 Ankara, Turkey situated in one of the most tectonically active regions of Asia 3 Department of Geological Engineering, Eskisehir Osmangazi Minor. Therefore, the area was destroyed several times by University, 26480 Meselik, Eskisehir, Turkey many earthquakes (Altunel and Barka 1996; Hancock and 4 Department of Geological Engineering, Pamukkale University, Altunel 1997; Altunel and Karabacak 2005;Kaymakci2006; Denizli, Turkey Uysaletal.2007, 2009;Keleetal.2011; Hancer 2013;De 1360 Archaeol Anthropol Sci (2019) 11:1359–1371

Filippis et al. 2012;Kumsaretal.2016). Directly build upon paralleling each other (cf. Özdemir 2002;Kaymakci2006; such a fault are two interesting buildings: the famous Apollo Hancer 2013;Kumsaretal.2016). Several buildings of temple and the newly discovered Plutonium, the sanctuary of Hierapolis were directly built on the fracture zone. Two buildings the Gods of the Underworld, Pluto and Kore, with the theater that were already mentioned by ancient writers for their Bdeadly above a grotto. The latter was excavated between 2011 and Hadean breath^ were selected for a close determination of 2013 during the campaign of the Italian Archaeological geogenic gas emissions: the Apollo temple and the newly exca- Mission in Hierapolis (D’Andria 2013). To be exact, this site vated sanctuary of Pluto (Fig. 1c; see also D’Andria 2013). has been mentioned by several antique sources as the entrance to the Underworld (Zwingmann 2012); they describe that Gas measurements strange things happened at this Hadean outlet which they called Plutonium (Ploutonium) or Charonium. Deadly vapors were Measurements were taken during two different campaigns in described escaping from these places (Strabo XIII, 4, 14; May 2013 and June 2014.The gas measurements were carried Bejor 1984). Priests were demonstrating their supernatural out with the portable gas analyzer GA2000 (Geotechnical power and their equality to the gods by ushering animals like Instruments, England; Pfanz et al. 2004) equipped with water goats and bulls into the grotto (Plutonium) where, after a short and dust filters. CO2,CO,CH4,H2S, and O2 were recorded time, the animals showed signs of suffocation, finally dying simultaneously. Problems occurred when the soil was wet, wa- after several minutes. Yet, the castrated priests (Galli) survived terlogged, or filled with hot water vapor, as liquid water would (Strabo XIII, 4, 14; Plinius, Nat. Hist. II, 207–208; for reviews, damage the sensitive cells of the analyzer. Polyethylene and see Zwingmann 2012 or Pfanz et al. 2014). Teflon tubing (1 cm in diameter) was used to enlarge the mea- Many similar sacred Greek and Roman places, oracles, and suring radius up to 6 m. Readings were recorded after several temples were often located directly above or close to geolog- seconds to one minute. Long-term measurements for CO2 were ical disturbance zones (Piccardi 2000;DeBoeretal.2001; made using a self-made CO2 analyzer,equippedwithanultra- Etiope et al. 2006; Foster and Lehoux 2007; Piccardi et al. low power (3.5 mW), non-dispersive infrared (NDIR) sensor

2008;Mariolakosetal.2010). The famous oracle of Delphi (measurement range of 0–100%; COZIR, CO2 Meter, Florida). was built on the intersection of two fracture zones where either The warm-up time of the sensor is shorter than 10 s; operating methane/ethylene venting or hypoxic aeration due to methane conditions are − 25 to 55 °C and 0–95% RH, non-condensing. or CO2 emission enabled Pythia to give her prophecies (De The accuracy of the sensor is ± 0.5% vol. CO2, at standard tem- Boer et al. 2001; Etiope et al. 2006; Piccardi et al. 2008). perature and pressure. The pressure dependence of the sensor is Heavy methane emissions were also found at Chimera 0.13% of the readings per millimeter of Hg. (Etiope et al. 2006; Hosgormez et al. 2008). In all cases, either The sensor was attached with a micro-diaphragm gas sample high CO2 concentrations or methane and other hydrocarbons pump (delivery, 0.4 l/min; KNF Neuberger, Balterswil, were emitted from geogenic sources (for a review, see Pfanz Switzerland). The sampling time was set with a microcomputer et al. 2014 and Etiope 2015). to 30 s. At the end of each interval, the measurement value was This paper accounts for the geochemical compositions of saved on a micro-SD card and the sensor and pump were pro- soil gas of some fractures and holes around the Hierapolis grammed to go to sleep mode until the next sampling cycle (after fault and Hierapolis archeological sites. We concentrated our 5 min). The battery-driven device was mounted within a water- survey specifically on the close vicinity of the Temple of tight hard plastic box. CO2 measurements at different heights Apollo and the Plutonium of ancient Hierapolis/Phrygia (15, 40, 100 cm) above the ground level within the sanctuary where mystic tales and narratives of the asphyxiation of bulls of Pluto were performed on different days in 2014. during religious ceremonies exist. We tried to (1) find and (2) In situ radon measurements were carried out by GEO-RTM quantify the noxious gas(es) inside and outside of the both 2128 alpha spectroscopy instrument. A Teflon tubing was temples and (3) examine the diurnal degassing patterns to help inserted 2–3 m into the mouth hole of the Apollo temple and understanding how ancient ceremonies were safely performed grotto of the Plutonium; it was directly connected with the radon by the priest of the sanctuaries. measurement chamber. The relative statistical error for radon activities ranged from over 10% for low radon values (∼ 2– 10 Bq l−1) to less than 5% for values greater than 10 Bq l−1. Material and methods The measurement period was selected as a minimum of 1 h to obtain reliable results with a high confidence level (95%). The The location isotopic composition of helium and neon was determined by mass spectrometry at INGV-Palermo. Two gas samples taken Hierapolis is located in the Denizli graben in the southwest of directly from the mouth of the grotto were collected by taking Turkey (Fig. 1a, b) which is a geological disturbance zone ex- care to avoid the least amount of atmospheric gas contamination. tending between the Pamukkale and Babadag faults that are The sampling procedure for free gases is as follows: free gases Archaeol Anthropol Sci (2019) 11:1359–1371 1361

Fig. 1 Location of the area of Hierapolis/Denizli in southwest Turkey (a). given (b). Known faults and grabens in the Denizli graben and its rims Position of the two sanctuaries, the sanctuary of Pluto (Plutonium) and the including the towns of Hierapolis, Laodikea, and Denizli. Maps were Temple of Apollo (top left) in the centrum of the Hierapolis excavated modified from Kumsar et al. 2016 (c) area. The positions of sinkholes in the close vicinity of the sanctuaries are were collected into the pyrex bottle having a three-way valve (for 3He/4He and 4He/20Ne). Uncertainties in the range of low connected to a silicon tube which was inserted into the grotto. 3He (R/Ra values below 0.1) samples are within ± 5% (Italiano The silicon tube was then connected to a syringe which sucked et al. 2013). the gas through the valve directly into the sampling pyrex bottle. The 3He/4He ratios (R) have been normalized to the atmo- To ensure pure geogenic gas, the bottle was flushed with a gas sphere (3He/4He = 1.39 × 10−6 = Ra) and corrected for the effects volume ten times larger than its own volume. For the final gas of atmospheric contamination (R/Rac) using (R/Rac) = {(R/Ra) collection, the first valve was closed and by applying a slight X − 1} / {X − 1} where X is the air and the ASW He/Ne ratio overpressure insight the bottle; the second valve was finally (Hilton et al. 1998). closed (Italiano 2009 and Italiano et al. 2013). Local weather data were obtained from the Turkish State Chemical analyses were done by gas chromatography Meteorological Service (DMIGM) for Denizli. (Perkin Elmer Clarus 500 equipped with a double TCD-FID detector) using argon as the carrier gas. Uncertainties were within ± 5% (Italiano et al. 2013). The isotopic compositions Results of helium were obtained by mass spectrometry. The isotopic analyses of the purified helium fractions were performed by a The new Plutonium—a deadly gas atmosphere split flight tube static vacuum mass spectrometer around and within the sanctuary of Pluto and Kore (GVI5400TFT) that allows the simultaneous detection of 3He and 4He-ion beams, thereby keeping the 3He/4Heerrorofmea- DuringtheexcavationheldbyD’Andria in 2011–2013, a sub- surement to very low values. Air is routinely run as a standard terranean grotto was found below the stone-seats of the for calibration. In general, the total errors on the ratios are less Plutonium (Fig. 2a). The grotto belongs to the sanctuary of than 2 and 5% in one sigma standard deviation, respectively Pluto (Hades) and Kore (Persephone). The words BPloutoni kai 1362 Archaeol Anthropol Sci (2019) 11:1359–1371

Fig. 2 Stone seating rows for the spectators of the ceremonies as seen in the freshly excavated Plutonium within the Sanctuary of Pluto, picture from 2013. The antechamber in front (blue arrow) of the subterranean grotto (white arrow) is seen. Also shown is the hole within the walls of the grotto where the geogenic gas escaped from the interior to the atmosphere (red arrow) (a). A similar scene of the Plutonium made in 2014 when excavations had finished and the proper basement was fully freed (b)

Kore^ in Greek letters engraved into the stone row below the chamber (grotto) of the Plutonium were performed by seats are still readable (D’Andria 2013). Due to the incomplete inserting a 6-m long Teflon tubing into the small opening excavation state of the Sanctuary in 2013, only the small, upper of the excavated wall (arrow in Fig. 2a). At a depth of part of the grotto and the antechamber was accessible for gas 2m,maximumCO2 concentrations inside the grotto were measurements (Fig. 2a). In 2013, access to the interior of the 91%. Measurements were herewith done at the mystical subterranean grotto was possible only through a small mouth place where hellhound Kerberos is expected to have its hole (red arrow in Fig. 2a). One year later (in 2014), the lower guard post (Bloomfield 1904). Yet, due to the small part of the Plutonium was fully excavated and freed the old mouth hole and the total darkness inside the grotto, the basement (Fig. 2b). Unfortunately, hot, carbonate-rich water exact position of the end of the tubing could not exactly poured into this basement from the interior of the grotto. The be located. The complete basement of the grotto was to- whole front area below the seat rows was thus flooded with water tally dark but seemed to be warm and highly humid (due up to a height of 10 cm. Thus, proper CO2 gas measurements to a warm carbonate-rich creek). were only possible above the water phase (ca. 15 cm All CO2 measurements within the grotto gave similar aboveground). results, independent of the exact position of the tubing. A rather homogeneous gas lake was therefore assumed with-

Gas data from the 2013 campaign in the grotto with more or less constant CO2 concentrations ranging between 86 and 91%. As neither wind nor Due to the incomplete excavation state of the Plutonium sun could enter the closed grotto, no large changes of the in 2013, gas measurements inside the closed subterranean gas concentrations were to be expected. Only close to the Archaeol Anthropol Sci (2019) 11:1359–1371 1363

small wall opening, CO2 concentrations slightly decreased. Due to some mixing with the normal atmosphere outside, around 74% CO2 were seen. Due to the extreme CO2 concentrations within the grotto, oxygen concentrations were well below ambient; only 6–2% O2 were found within the grotto, the rest being nitrogen (N2). The situation was totally different for the sanctuary’sfloor, the antechamber outside the grotto (Fig. 2a; blue arrow). Surrounded by walls, which prevented the rapid discharge of the gas, the floor was continuously flooded with CO2 during the whole day. As CO2 is 1.5 times heavier than air, the escaping CO2 gas forms a gas lake at the floor (Pfanz et al. 2014, Kies et al. 2015). Depending on atmospheric and microclimat- ic conditions, the CO2 gas lake on the floor of the antechamber varies diurnally. It has again to be mentioned that due to the Fig. 3 Gas victims in front of the grotto. The beetles were killed during incomplete excavation state of the Plutonium in 2013, the the high-CO2 phase of the gas lake persisting through the dark hours. As a location of the floor does not represent the original proper very thin gas lake (up to 5 cm in height) also exists during daytime, floor level (but see Fig. 2b). Yet, even at this higher level of insects also suffocate during sunny hours. Dead beetles were from several families: Tenebrionidae, Carabaeidae, and Scarabaeidae the floor, a small gas lake existed. It has to be stressed that a deadly CO gas lake existed only under certain weather con- 2 this is the persistent thin gaseous CO coat that covers the ditions: no direct sunlight and no strong air movement. On 2 lowest 5 cm of the very bottom throughout the day. sunny or windy days, no gas lake was measurable during daytime but occurred through the night. Yet, measurements of the gas lake performed during early Data from the 2014 campaign morning hours clearly proved the presence of CO2.Although it was mostly slightly windy during our first campaign, the Due to the advanced excavation state of the lower part of actual CO2 gas lake had a maximum height of 35 cm above the sanctuary (Fig. 2b), diurnal gas fluctuations within the the floor of the antechamber with CO2 concentrations antechamber of the Plutonium could be measured contin- reaching 57% at the very bottom. As expected, CO2 concen- uouslyin2014(Table1). As the floor was flooded with trations dropped with height due to wind dilution. At 10 cm water from a thermal creek, the gas analyzer was posi- aboveground, CO2 was reduced to 36% and further declined tioned at three different heights above the floor of the via 9.0 and 3.9% CO2 at a height of 20 or 30 cm, respectively. antechamber: (i) directly above the water level (15 cm; At 40 cm above the ground level, measured CO2 concentra- on stones which emerged from the water table) or (ii) tions were close to ambient (0.04–0.05% CO2). At the same 40 cm or (iii) 100 cm aboveground. The data given in time, oxygen values increased from 8.0–9.3% at the very bot- Fig. 4 show the differences of the diurnal CO2 gas re- tom via 12.7 and 18.7 to finally reach 19.3–20.7% at 40 cm gimes at these heights. Varying the height of the measure- height. During all morning hours, observed CO2 concentra- ments, the potential threat of the deadly gas to different tions at the very bottom of the antechamber of the Plutonium organisms could be simulated. Furthermore, continuous were always in the range between 27 and 76%. At the same measurements exactly proofed at which time of the day time, oxygen values were very low (6.6–12.5%). The reason the highest danger was to be expected. As only one CO2 for the broad concentration range of both gases was the fluc- device was available, the data at different heights repre- tuating wind and solar irradiation. sent different days (Fig. 4).

In addition, the great number of corpses of insects and When the CO2 analyzer was mounted 100 cm above the birds corroborated the existence of a deadly CO2 gas lake ground of the antechamber, nearly no excess concentrations of in front of the grotto. On our first day, two dead birds and CO2 were found during a diurnal cycle (Fig. 4). Measured data more than 70 dead beetles (Tenebrionidae, Carabaeidae, ranged between 0 and 5% CO2. Nevertheless, it has to be and Scarabaeidae) were found asphyxiated at the floor mentioned that CO2 concentrations around 5% can lead to (Fig. 3). Locals report on dead mice, cats, weasels, and dizziness in humans if inhaled for longer than 5 min even asphyxiated foxes. Most animals are not killed dur- (IVHHN 2013). The picture was clearly different when the ing sunny days, but during the dark evening and morning CO2 monitor was placed closer to the ground (40 cm above- hours. For small organisms like insects, there is a danger ground). A dramatic increase of CO2 was now seen during the to get asphyxiated even during daytime; they were seen to dark hours. Depending on the prevailing wind and rain con- be asphyxiated even during midday hours. The reason for ditions, CO2 ranged between 2 and 36% (Fig. 4). Yet, in most 1364 Archaeol Anthropol Sci (2019) 11:1359–1371

Table 1. CO2 and radon concentrations as measured at ID Type Date Information Latitude Longitude Rn CO2 3 selected locations in the vicinity of (kBq/m ) (%) two Sanctuaries. Measurements were performed in 2014 F-1 Fracture 08/06/2014 Denizli-Hierapolis 37.92559 29.12652 46.880 96.30 F-2 Fracture 08/06/2014 Denizli-Hierapolis 37.92473 29.12670 0.128 0.38 F-3 Sinkhole 09/06/2014 Denizli-Hierapolis 37.92498 29.12681 19.500 22.40 F-4 Sinkhole 09/06/2014 Denizli-Hierapolis 37.92484 29.12651 – 0.10 F-5 Fracture 09/06/2014 Denizli-Hierapolis 37.92490 29.12630 – 0.10 F-6 Fracture 09/06/2014 Denizli-Hierapolis 37.92550 29.12626 – 0.07 F-7 Fracture 09/06/2014 Denizli-Hierapolis 37.92523 29.12686 – 16.40 F-8 Fracture 09/06/2014 Denizli-Hierapolis 37.92468 29.12699 – 0.15 F-9 Sinkhole 09/06/2014 Denizli-Hierapolis 37.92848 29.12469 – 4.50 F-10 Sinkhole 09/06/2014 Denizli-Hierapolis 37.92691 29.12546 87.150 36.00 F-11 Apollo 10/06/2014 Denizli-Hierapolis 37.92681 29.12686 162.070 60.00 F-12 Sinkhole 10/06/2014 Denizli-Hierapolis 37.92547 29.12708 13.950 51.30 F-13 Sinkhole 10/06/2014 Denizli-Hierapolis 37.92589 29.12714 – 65.70 F-14 Sinkhole 10/06/2014 Denizli-Hierapolis 37.92571 29.12712 103.000 81.40 F-15 Sinkhole 12/06/2014 Denizli-Hierapolis 37.92708 29.12684 50.40 Plutonium 08/06/2014 Denizli-Hierapolis 37.92625 29.12704 6.500* 6.40* 08/06/2014 Denizli-Hierapolis 22.210** -

*in air **in waterFF-9

time of the day, concentrations were below 10% CO2.Those stable. But even during daytime, concentrations were concentrations will asphyxiate and kill humans and oth- rather high (5–20%) but they still increased in the eve- er mammals within minutes. Even higher CO2 concen- ning hours to reach maximum levels during late evening trations were reached with the monitor placed directly and night (Fig. 4). Deadly 68% CO2 were then mea- above the water phase of the antechamber’s floor sured in the atmosphere close to the bottom (sometimes

(15 cm above the proper floor). During the, night ex- even 85% CO2; not shown). During morning hours, tremely high CO2 were found (Fig. 4). The diurnal CO2 these concentrations were quickly reduced due to solar concentrations were neither constant nor were they irradiation (see also Kies et al. 2015).

Fig. 4 Diurnal courses of the CO2 gas concentrations in front of the weather at these days was quite similar. Rather hot and sunny during antechamber of the grotto within the sanctuary of Pluto. Measurements daytime (temperatures up to 38 °C) and strong rain events and were performed for 24 h (from 09.00 p.m. to 09.00 p.m.) at three different thunderstorms in the afternoon or during the night. As only one CO2 heights aboveground (lowest level 15 cm; medium level 40 cm; and device was available, the data at different heights represent different upper level 100 cm). Measurements at the proper ground level were not days. Average temperature and wind speed are given. Rainfall events possible as the base of the antechamber was flooded with water draining are marked in red. Rainfall and wind speed values are exaggerated by a from the hot carbonate creek running downhill through the grotto. The factor 10 Archaeol Anthropol Sci (2019) 11:1359–1371 1365

Radon concentrations in both temples (9 and 55 kBq m−3) atmosphere is known and the entrance to the cellar below can be considered as higher than normal since they are located the temple was therefore firmly walled due to safety reasons. in the same active fracture zone. Radon concentrations mostly When the Teflon-tubing was inserted 2–3 m into the mouth paralleled the concentrations of geogenic CO2 (Table 1). This hole of this grotto, between 60 and 65% CO2 were to be behavior is understandable as radon is transported from its measured independent of the exact location of the tubing. At geological source within a matrix of CO2 as the carrier. It the same time, oxygen was around 8–8.5%. Also, here, like in becomes clear that geogenic gas emissions frequently occur the neighboring new Plutonium, a deadly geogenic CO2 at- within the fracture zones of the graben structure cutting its mosphere accumulates within a walled chamber. And again, way through ancient Hierapolis. this gas emission reflects the breath of the deadly underworld Aside from carbon dioxide, other gases could also be mea- in ancient times. Because the originally existing larger open- sured within the grotto, but only in very low concentrations. ing had been sealed due to safety considerations, no enhance-

Carbon monoxide was present in minute concentrations (1– mentofCO2 concentrations could be observed outside the 3 ppm) and oxygen concentrations were down to 3.2%. hole. Methane and hydrogen sulfide were absent, whereas radon concentrations were found to be between 50 and Geogenic gas in the closer surroundings of the two 55 kBq m−3 in both places. The chemical analysis (Table 2) sanctuaries is also consistent with the in situ measurements. The air corrected helium isotope ratios of the two samples are 3.61 Since both sanctuaries are located in the same seismic fracture and 3. 78 Rac, respectively. These values are consistent with a zone of the Hierapolis fault (De Filippis et al. 2012). Gas previous work of Ercan et al. 1995 (air corrected R/Rac = analyses were enlarged to the close vicinity of the temples. 3.68) and Gulec et al. 2002. The concentration of helium is Therefore, some measurements were performed within the above the atmospheric value and CO2 is the dominant gas linear fracture zone east and west of the two sanctuaries possibly carrying mantle sourced helium. The relationship (Fig. 6a). Several CO2-emitting spots were found in sinkholes between 3He/4He and 4He/20Ne ratios shows mixing curves in the vicinity of the sanctuaries (Fig. 6b). In the south of between atmospheric and mantle/crustal components (Fig. 8) Pluto’s sanctuary along the graben lineament, gas concentra- 3 4 assuming that an atmospheric component has He/ He = tions of up to 84% CO2 were measured in small crevices. −6 4 20 1.39 × 10 and He/ Ne = 0.318, and a crustal component Increased CO2 was also found in the seismic graben structure has 0.02 Ra and 4He/20Ne = 1000 (Sano and Marty 1995). itself but also in sinkholes around the fracture zone. Yet, the

The presence of different mantle-type components is also con- highest CO2 concentrations were found within the grotto of sidered: MORB-type mantle with 8 Ra and 4He/20Ne = 1000, the sanctuary of Pluto and at a sinkhole some 25 m east of the sub-vontinental European mantle (SCEM, Dunai and Baur sanctuary. Geogenic CO2 decreased in southeast and north- 1995) R/Ra = 6.5 and 4He/20Ne = 1000. The mantle contribu- west directions, although concentrations were still deadly until tion was calculated about 75% (Table 2) and the radon content locations F3 (141 m) and F15 (92 m; Fig. 7a, b). The fractures in the gas samples confirmed deep origin with remarkably and sinkholes in the close vicinity of the two sanctuaries are higher values. It is obvious that this higher helium isotope not evenly distributed; therefore, the sites for gas measure- ratio with an elevated CO2 and radon content strongly hint ments had to be adapted to the local settings. Since the survey to the tectonic activity and proves the ascent of mantle vola- was focused on the closer vicinity of both temples, more dis- tiles to the surface. Moreover, the N2/O2 ratio is well above tant natural springs and fractures were excluded. that of atmospheric ratio (~ 2) which is consistent with the higher helium isotope ratio (Table 2). Discussion

The old Plutonium—geogenic gas below the temple Physical and meteorological behavior of geogenic of Apollo CO2

Similar findings were obtained when the grotto below the Within the two sanctuaries of Apollo and Pluto, geogenic CO2 temple of Apollo was studied. The sanctuary of Apollo is was found in subterranean chambers (D’Andria 2013). These situated 200 m west of the sanctuary of Pluto within the same grottos were situated either below the proper temple (in the seismic fracture zone due to the extension of the fault line and case of the Apollo temple) or below the seating rows for the it is long known for its subterranean grotto-like structure pilgrims and spectators (in the case of the sanctuary of Pluto).

(Figs. 1 and 5). This cellar-like chamber below the Apollo In both cases, more than 60% CO2 accumulated within the Sanctuary is marked as BPlutonium^ in touristic guides of walled grottos as neither sunlight nor wind was able to dilute Hierapolis (D’Andria 2003). The toxicity of its gas this poisonous atmosphere. 1366 Archaeol Anthropol Sci (2019) 11:1359–1371

Table 2 Gas analysis of the Pamukkale spring as determined by the Noble Gas Laboratories of INGV, Palermo

Sample ID He O2 N2 N2/O2 CO CO2 R/Ra He/Ne [He] Corr [Ne] Corr R/Rac Mantle Contribution Rate

%Atm %Rad %Mag

Pamukkale 1 0.0011 3.3 17.9 5.42 0.0005 80.38 3.25 2.290 8.094 3.535 3.61 11.6 13.69 74.68 Pamukkale 2 0.0012 3.43 18.45 5.38 0.0003 80.65 3.33 1.965 6.213 3.162 3.78 13.6 8.52 77.91

The gas that permeated through cracks and holes to the and final dissipation within the above-lying air parcels. outside of the grotto of the sanctuary of Pluto showed a dif- Similar observations have been made for a larger, natural ferent behavior. Due to the higher density of CO2, the diurnal CO2 gas lake in Italy (Kies et al. 2015). Furthermore, a buildup of a CO2 gas lake occurred on the very bottom in front closer look to Fig. 4 shows that even within this diurnal, of the grotto. sinus-like BCO2 wave^ of the gas lake, concentrations CO2 concentrations in the antechamber of the grotto were not ideally stable for a longer period. A heavy scat- located directly ahead of the sitting rows for spectators terofCO2 concentrations mainly during night hours is and pilgrims were highest close to the bottom (Fig. 4). seen (Fig. 4). Concentrations varied from 68 to 10% CO2 With increasing height, CO2 concentrations decreased. within minutes. The reason for these sudden CO2 changes Furthermore, sunlight, temperature, and wind induced a were wind gusts and heavy rain events occurring during diurnal pattern in the gas lake of the antechamber. our measurement campaign (see also Bettarini et al. Within the antechamber, the formation of a higher- 1999; Etiope et al. 2005;Pfanz2008;Kiesetal.2015). concentrated CO2 gas lake occurred only during the dark Meteorological data compiled from the region are well hours of calm nights. Under windy conditions or during consistent with the CO2 data. There is an inverse relation- the sunny hours of a normal day, the gas lake was partial- ship between the CO2 gas concentration and air tempera- ly or wholly destroyed due to the strong infrared absorp- ture, rainfall, and wind causing a CO2 decrease (Fig. 4). tion of CO2 and the concomitant heating of the system (Pfanz et al. 2004, 2014). The heating of the gas lake leads to a decrease of its density and to its disintegration

Fig. 5 Radon measuring set in front of the closed chamber of the Apollo temple. The CO2-filled room below the temple has been sealed by walls. Fig. 6 Fracture zone thorough a travertinic rock east of the sanctuaries Gas measurements were therefore made by inserting the tubing through (a). Gas tubing was inserted into a sinkhole in the vicinity of the the small window that was left open sanctuaries (b) Archaeol Anthropol Sci (2019) 11:1359–1371 1367

Fig. 7 Location of the different measuring points of CO2 and radon contents within the settings of the two sanctuaries of Apollo and Pluto. The points were selected according to the morphology of the site and the direction of the fissure (a). CO2 and radon concentrations as measured at the locations given (b). Data from both campaigns in 2013 and 2014. CO2 concentrations are given in percent; radon is given as kBeq/l.

Gate to hell—the historical relevance of the gas within the grotto of Plutonium. Neither mammals nor reptiles findings or birds can survive. Even insects are killed within minutes (for some exceptions, see Russell et al. 2011). Outside the

Biological effects of extreme CO2 concentrations grottos, in the antechambers, the situation is different. Depending on the size/height of the respective animal (and Several old writers report on the death of birds, rams, and bulls depending on the time of the day and the weather condition), in the vicinity of the two Plutonia. The measured data clearly the situation could be either deadly toxic or only slightly dan- proof that even nowadays, CO2 concentrations and the con- gerous. Mammals already react to CO2 concentrations as low comitant low oxygen concentrations within the grottos and as 3–5%. Even these rather low concentrations may increase antechambers of the sanctuaries of Pluto and Apollo are high- cardiac frequency and respiratory rate if incubation time is ly toxic. So clearly, oxygen-depending life will not exist longer than several minutes (D’Alessandro 2006;Pfanz 1368 Archaeol Anthropol Sci (2019) 11:1359–1371

2008). At CO2, concentrations around 8–10% humans are It is also known from other authors that sacred Greek and asphyxiated and a longer incubation at 15–20% inevitably Roman oracles and temples were often located on or close to leads to death (IVHHN 2013). geologically active zones (De Boer et al. 2001; Etiope et al. 2006;Piccardietal.2008; Mariolakos et al. 2010).

Historical relevance of the gas findings Understanding the principle of sacrificing bulls, rams, Entrance to hell and birds

To the ancient people, these gas-emitting places were extreme- The toxic atmosphere around these sites lead Greeks and ly frightening and therefore holy and consecrated. Such sites Romans to believe that these places, called mephitic caves were often found just accidentally by herdsmen or farmers or mephitic locations, were the entrance to the ancient watching their cattle behaving strange. Herdsmen were astute underworld, the Hades, the ancient gate to hell in observing nature; even a slight change or variation in the (Plutonium, Charonium; see Piccardi 2007;CassiusDio, normal vegetation (Pfanz et al. 2004) could alert them to such n.d, Plinius, n.d, Strabo, n.d). As there were celebrations extraordinary places (Pfanz et al. 2014). Often temples and and festivities, ancient tourists, pilgrims, and spectators sanctuaries were then erected at these sites. These sacred sites were attracted. Even at this time, tourism was sophisticat- resembled the entrance to the Underworld, the antechambers ed as not only accommodation and food was provided, of the Hadean. Deadly vapors were escaping from these out- but also living animals for sacrifice and other attractions lets (Strabo XIII, 4, 14). The toxic vapors resembled either the were sold. The spectators of the religious presentations deadly breath of Pluto/Hades, the Greek god of the kingdom threw the freshly purchased birds down onto the ante- of the death or even more plausible the breath of the frighten- chambers floor (into the invisible gas lake) where the tiny ing hellhound Kerberos guarding the entrance to hell. creatures quickly died (Zwingmann 2012). Even more im- Furthermore, these places were also the sites were Pluto pressive were the effects of the Hadean atmosphere when abducted Persephone, the daughter of Demeter (see also a larger animals were sacrificed. On special events and sa- similar site in Greece, Eleusis; Von Uxkull 1957). The already cred days, bulls and rams were also ushered into the an- terrifying impression of Hadean entrances is sometimes cor- techambers of the sanctuary. Young men had carried the roborated by evaporating steam pouring out of holes and sacrificial animal to the sanctuary (see coin found at cracks on cold days. This is also true for the Plutonium at Acharaka; Von Diest et al. 1913). While the bull was the Sanctuary of Hierapolis; a hot carbonate-rich, below- standing within the gas lake with its mouth and nostrils ground creek is the cause of it (Fig. 2b). at a height between 60 and 90 cm, the large grown priests

Fig. 8 Helium and neon isotopic ratios given as R/Ra values and He/Ne relationships, respectively. The theoretical lines represent binary mixing trends of atmospheric helium with mantle- originated and crustal helium. The assumed end-member values for He isotopic ratios mark the mixing curves: crust 0.02 Ra and three different mantle-signatures: 8 Ra (MORB), 6.5 Ra (SECM), and 4 Ra for a contaminated/ degassed mantle Archaeol Anthropol Sci (2019) 11:1359–1371 1369

(Galli) always stood upright within the lake caring that Acknowledgements We want to thank the governorship of Denizli City their nose and mouth were way above the toxic level of for their kind help. We are indebted to Omer Faruk Gunay, vice governor of Eskisehir City, and Ismail Soykan, vice governor of Denizli City. The the Hadean breath of death. It is reported that they some- great help of the director of Hierapolis/Pamukkale is greatly acknowl- times used stones to be larger. The spectators could see edged. The authors wish to extend their sincere thanks to the provincial that animals as strong, sturdy, and powerful as bulls died culture and tourism directorate of Ankara and Denizli. Dr. Francesco within minutes whereas the priests survived (for an Italiano kindly provided data about gas analysis from the grottos. Special thanks to Dr. Christiane Wittmann and Volker Wittmann for their overview see Pfanz et al. 2014). Many ancient writers excellent work in building a robust, continuously recording CO2 monitor. discuss the survival of the Eunuch priests and state either The authors are also grateful to Selami Yildirim and Mehmet Ergun from the godlike powers of the Galli, the application of anti- the Turkish State Meteorological Service. The authors are extremely ’ dotes and/or other precautions to survive the deadly gas thankful to Prof. Dr. Francesco D Andria, who detected and excavated the new Plutonium at Hierapolis for his kind help providing a permission (Cassius Dio, Epitome 68.27.2 and 3; for details see to work on the site, to his intelligent advices and to his permanent interest Zwingmann 2012). It seems pretty clear that the priests in the progress of our study. were fully aware of the gas and also of its physicochemical properties. They were aware of the diurnal changes of the deadly vapors and they were aware of the varying References height of the gas lake. 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