Uchida et al. Herit Sci (2017) 5:42 DOI 10.1186/s40494-017-0155-0

RESEARCH ARTICLE Open Access Determining the construction sequence of the monument in from its sandstone block characteristics Etsuo Uchida1* , Akinori Mizoguchi2, Hiroya Sato1, Ichita Shimoda3 and Ryota Watanabe1

Abstract The Preah Vihear monument in Cambodia, located close to the border with , was one of the Khmer temples registered on the UNESCO World Heritage List as a Cultural Property in 2008. It consists of masonry buildings con- structed of siliceous sandstone blocks. In this study, the construction sequence of its buildings was inferred from the chemical composition, magnetic susceptibility, and size of the sandstone blocks, along with pediment end style, and the presence or absence of reliefs on the tympana of adjacent buildings. Five construction stages were identifed. We revealed that the Western Annex Hall (N2) is the oldest edifce in the Preah Vihear monument. We also reconfrmed that the Preah Vihear monument was constructed over a range of years, spanning the Bakheng style period to the Wat style period (the end of the 9th century to the end of 12th century). It was clarifed that during the con- struction of Preah Vihear, the style of pediment ends changed from pediments ending in scrolls made from one block, to pediments ending in scrolls made from two blocks, and fnally to pediments ending in fve-headed nagas. Over the same time span, the size of the sandstone blocks used in construction increased markedly. Keywords: Preah Vihear, Sandstone, Chemical composition, Magnetic susceptibility, Portable XRF, Construction sequence, Cambodia

Background [11], and Sahai [12]. Tese studies were conducted from Te Preah Vihear monument in Cambodia is located near architectural and art-historical viewpoints or based on to the border with Tailand (it is called Khao Phra Wihan inscriptions. Te Preah Vihear monument is believed in Tailand), on the southern margin of the Khorat Pla- to have been constructed by the between teau (Fig. 1) [1–3] and consists of masonry buildings the 9th and 12th century AD. Groslier [8] and Parmen- constructed from sandstone blocks. Te monument was tier [9] considered that the Preah Vihear monument con- occupied by since 1989 and released in sisted originally of wooden buildings and they were later 1998. Te maintenance of the monument was conducted replaced by masonry buildings. by the Cambodian Government during 2000–2002. Te Parmentier [9] and Sahai [12] created construction monument was designated as a UNESCO World Cultural chronology of the Preah Vihear monument based on Heritage Site in 2008. architectural evidences and inscriptions, respectively. Te study of the Preah Vihear monument was initi- Te construction chronology inferred by them is based ated by Barth [4] and Bergaigne [5] and then followed on unclear architectural traces and limited inscriptions, by Aymonier [6], Lunet de Lajonquiere [7], Groslier leaving room to be reconsidered. In contrast to the pre- [8], Parmentier [9], Cœdès [10], Jacques and Freeman vious studies, this study infers objectively the construc- tion sequence of the monument based on its building stone characteristics such as the chemical composition, *Correspondence: [email protected] magnetic susceptibility, and size of the sandstone blocks, 1 Department of Resources and Environmental Engineering, Waseda University, Ohkubo 3‑4‑1, Shinjuku‑ku, Tokyo 169‑8555, Japan taking into account architectural, iconographic and epi- Full list of author information is available at the end of the article graphic evidences.

© The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Uchida et al. Herit Sci (2017) 5:42 Page 2 of 15

Fig. 1 Location of the representative Khmer monuments, including the Preah Vihear monument [1]. The provenance of sandstones used for constructing the Khmer monuments is also shown in this fgure [2, 3]. The colored asterisks for each monument are correlated with the various sandstone formations used to construct them

Buildings in the Preah Vihear monument on terraced slope as well as the Wat Phu temple in . Te faces north and is located on Te distance between the north entrance and the south a slope of the Dangrek Range that increases in altitude end is approximately 800 m. from the north entrance (550 m above sea level) to the Te buildings of the Preah Vihear monument are southernmost end (630 m above sea level), with a relative arranged in four groupings (Fig. 2). Te names and sym- height of 500 m above the plain of Cambodia. Te Preah bols used to identify its constituent buildings are from Vihear temple is a horizontally–oriented layout temple Roveda [13]. Te southernmost group is the largest, and Uchida et al. Herit Sci (2017) 5:42 Page 3 of 15

Fig. 2 Plan view of the Preah Vihear monument [13], showing the name and symbol of each building. The fve construction stages established in this study based on sandstone characteristics and pediment end style are shown as diferent colors, grading from blue to red, corresponding to oldest to newest edifces. Arrows indicate the construction sequence with respect to adjacent buildings

consists of the South Gopura (A) (Fig. 3a), Central Sanc- (K1 and K2), and Gopura II (L). Relatively large sand- tuary (B), Mandapa (C), Gallery (D) (Fig. 3a), Western stone blocks were used in the South Gopura (A), Central Building (E), Eastern Building (F), Gopura I (G), Librar- Sanctuary (B), Eastern Building (F), part of the Gallery ies (H1 and H2) (Fig. 3b), Hall (J), L-shaped Galleries (D), and part of the Western Building (E). In addition, Uchida et al. Herit Sci (2017) 5:42 Page 4 of 15

Fig. 3 Photographs of (a) South Gopura (A) and Gallery (D), (b) Eastern Library (H1), (c) Gopura III (P), (d) Gopura IV (T), (e) ancient sandstone quarry for large sandstone blocks situated in the south of South Gopura (A), and (f) ancient sandstone quarry situated in the west of the causeway between Gopura IV (T) and Gopura V (W). Sandstone blocks used for these building have a yellowish-brown color

bedrock was used for part of the Gallery (D) and Western the fourth group only of the Gopura V (W). Te upper Building (E). structure of the Gopura V (W) has almost collapsed. Te second group from the south is the second larg- est, and consists of the Annex Halls (N1 and N2) and Methods U-shaped Extensions (O1 and O2) and Gopura III (P) Magnetic susceptibility of the sandstone blocks was (Fig. 3c). Bedrock was used for part of the platform of the measured using a portable magnetic susceptibility meter Western Annex Hall (N2). A small Tower (Q) is located (ZH instruments SM30, Brno, Czech Republic), with a north of the Eastern U-shaped Extension (O1). Te third reading surface of 5 × 5 cm. Measurements were made group consists only of the Gopura IV (T) (Fig. 3d), and on 50 fat surfaces in each section of each building of the Uchida et al. Herit Sci (2017) 5:42 Page 5 of 15

monument, and used to calculate average values. Care I (G), Hall (J), Gopura II (L), and Gopura III (P) edifces was taken to avoid blocks covered with algae or lichen belonging to the fourth stage have the highest values, −3 [14, 15]. with averages in the range of 0.049–0.068 × 10 SI units. Chemical analyses of the sandstone blocks were carried Te ffth stage buildings have low magnetic susceptibili- −3 out using a portable X-ray fuorescence analyzer (pXRF; ties, with averages in the range of 0.019–0.042 × 10 SI Innov-X Systems Delta Premium, Waltham, MA, USA), units. measuring in soil mode. Te instrument was calibrated using 10 reference rocks from the Geological Society of Chemical composition Japan (JA-1, JA-2, JB-1b, JB-2, JB-3, JG-1a, JG-2, JGb- Te following elements were quantitatively measured 1, JR-1, and JR-2) [16]. Measurement time was 1 min. using the pXRF: K, Ca, Ti, Cr, Mn, Fe, Cu, Zn, Rb, Sr, Y, Measurements for fve sandstone blocks in each building Zr, and Pb. Among these elements, K, Ti, Fe, Zn, Rb, and were obtained from fat surfaces, not covered by algae or Zr show systematic changes in content in the sandstone lichen. Tese values were averaged. blocks used during construction. Te contents of K, Ti, Te size of the sandstone blocks was determined along Fe, Zn, Rb, and Zr in the sandstone blocks are relatively wall surfaces, showing width and thickness. Dimensions low in the frst and third stages, but high in the second were measured for 25–50 sandstone blocks in each sec- and fourth stages. Tey have intermediate values in the tion of each building of the monument, and averaged. ffth stage. In addition, bedding plane orientations in the sandstone In particular, the contents of Rb and Ti changed mark- blocks were recorded. edly. In the frst and third stage edifces, their contents Tree diferent types of pediment end styles were rec- had ranges of 20–30 and 1050–1100, and 22–28 and ognized in the Preah Vihear monument. We investigated 800–1000 ppm, respectively. Teir contents were higher the pediment end style in each building to clarify the in the second stage (33–45 and 1240–1510 ppm) and relationship with the construction period. the fourth stage (37–44 and 1330–1480 ppm). Te ffth stage had the low to intermediate contents (18–34 and Results 1000–1360 ppm). Te results of magnetic susceptibility and pXRF measure- ments are summarized in Table 1, along with information Block size on block size and pediment end style. Variation in these In Table 1, block size is listed as: “Small”, <50 cm in thick- parameters within the monument is discussed below. ness and <50 cm in width; “Medium”, <50 cm in thickness Te construction sequence (the frst to ffth stages) listed and 50–100 cm in width; and “Large”, >50 cm in thick- in Table 1, but described in more detail later, is inferred ness or >100 cm in width. Table 1 shows that block size from the chemical composition, magnetic susceptibility, became larger over the construction time. sandstone block size, pediment end style, and the pres- Te central part of the Western Annex Hall (N2), in ence or absence of relief work on the tympana of the contrast to other parts or other buildings, was con- adjacent buildings. structed with the smallest sandstone blocks in the Preah Vihear monument, having an average thickness and Magnetic susceptibility width of 35 × 43 cm. Likewise, the sandstone blocks used Te siliceous sandstone blocks used in the Preah Vihear in the platform of the Western Annex Hall (N2) are dis- monument have low magnetic susceptibilities, with aver- tinctly thin, having a thickness and width of 23 × 44 cm −3 age values in the range of 0.011–0.068 × 10 SI units. on average. In contrast, large sandstone blocks with In contrast, the gray to yellowish-brown sandstones used dimensions of 60–80 × 130–160 cm or larger were used in the Angkor monuments, which are feldspathic arenites in the Central Sanctuary (B), South Gopura (A), Eastern supplied from the southeastern foot of Mt. Kulen, have Building (F), Gopura IV (T), part of the Gallery (D), and higher average magnetic susceptibilities, with values in part of the Western Building (E). Medium-sized sand- −3 the range of 0.7–9.1 × 10 SI units [14, 15, 17, 18]. stone blocks were used in all other buildings. Te sandstone blocks of the central part of the Western Annex Hall (N2) (the frst stage) have the lowest mag- Bedding plane orientations netic susceptibility in the Preah Vihear monument, aver- In the upper structure of the central part of the West- −3 aging 0.011 × 10 SI units. Te magnetic susceptibility ern Annex Hall (N2), 54% of sandstone blocks have of the sandstone blocks of buildings in the second stage is vertical bedding planes. Many sandstone blocks with −3 high, averaging between 0.041 and 0.047 × 10 SI units. square ends are also observed in the platforms of the It is low in the third stage, with averages in the range of Eastern Annex Hall (N1) and U-shaped Extensions (O1 −3 0.023–0.045 × 10 SI units. Te Mandapa (C), Gopura and O2), and almost half of them have vertical bedding Uchida et al. Herit Sci (2017) 5:42 Page 6 of 15 block block block Style of pedi - ends ment Scroll, one Scroll, Scroll, one Scroll, Scroll, one Scroll, c ­ size Block Small Small Small Small Small Small Medium Medium Medium b Pb (1σ) 4.2 (1.8) 5.1 (0.8) 5.8 (1.9) 4.9 (1.9) 5.4 (2.4) 5.2 (1.8) 3.9 (0.6) 4.3 (1.9) 11 (6.3) b (11.9) (19.1) (22.7) (22.7) (31.9) (14.3) (40.3) 68.0 (56.2) Zr (1σ) 71.8 75.0 83.1 75.4 101.2 116.7 107.5 156.0 119.8 b Y (1σ) 12.2 (2.8) 10.2 (1.7) 13.2 (2.3) 12.0 (2.3) 15.3 (3.0) 15.7 (2.1) 17.0 (2.0) 18.5 (3.4) 14.3 (3.7) b Sr (1σ) 14 (2.9) 14 (2.0) 16 (3.3) 14 (1.8) 19 (1.0) 19 (3.0) 20 (3.5) 19 (1.6) 21 (7.4) b Rb (1σ) 24 (6.8) 20 (5.9) 30 (11.5) 20 (2.6) 44 (4.4) 41 (11.2) 33 (7.0) 42 (2.9) 36 (14.4) b Zn (1σ) 12.8 (4.4) 13.5 (8.3) 28.9 (3.3) 22.2 (3.3) 34.2 (10.6) 27.3 (3.5) 30.1 (10.6) 32.2 (5.1) 36.2 (17.0) b Cu (1σ) 10.4 (2.5) 13.8 (6.0) 25.8 (27.2) 11.0 (27.2) 13.2 (1.0) 19.4 (18.9) 29.2 (22.3) 15.0 (10.4) 21.6 (10.3) b (880) (2220) (1570) (2650) (1340) (1530) (640) (670) (2680) Fe (1σ) 11,800 9580 9500 11,800 11,500 11,600 10,600 11,400 12,400 b (156) (128) (128) Mn (1σ) 205 (18) 287 381 196 180 (14) 184 (19) 205 (40) 256 (94) 244 (67) b Cr (1σ) 33.6 (38.3) 13.4 (6.3) 19.8 (2.6) 19.8 (2.6) 35.4 (16.3) 31.6 (9.8) 23.2 (5.2) 23.0 (3.5) 21.4 (10.0) (80) (249) (205) (166) (107) (191) (322) (222) (405) b (1σ) Ti 1100 1050 1060 1070 1240 1360 1510 1430 1260 b (200) (450) (410) (410) (120) (2640) (330) (250) (220) (1σ) Ca 6300 6800 6760 6990 6210 8330 6660 6270 6300 (1980) (1720) (2450) (2450) (1560) (1000) (1750) (570) (3250) b K (1σ) 2690 2470 4260 3170 5510 7530 5990 6640 6060 a (0.009) (0.007) (0.010) (0.013) (0.019) (0.019) (0.021) (0.017) (0.025) MS (1σ) 0.011 0.015 0.018 0.014 0.042 0.042 0.047 0.043 0.041 Annex Hall (N2) cen - upper tral, structure Annex Hall (N2) central, platform Annex Hall (N2) east, lower platform Annex Hall (N2) west, platform Annex Hall (N2) east, upper structure Annex Hall (N2) east, upper platform Annex Hall (N1) U-shaped Extension (O2) L-shaped L-shaped Gallery (K2) platform Building Western Western Western Western Western Western Western Western Western Western Western Western Eastern Western Western Western Western Construction sequence for buildings of the Preah Vihar monument based on their sandstone block and pediment characteristics block and pediment based on their sandstone monument Vihar of the Preah for buildings sequence Construction style period: the end of the 9th cen - tury the to beginning of the 10th century) Khleang style period: the early 11th century) 1 Table Stage 1st (Bakheng 2nd (Late 2nd (Late Uchida et al. Herit Sci (2017) 5:42 Page 7 of 15 block block block blocks block blocks blocks blocks blocks headed naga Style of pedi - ends ment Scroll, one Scroll, Scroll, one Scroll, Scroll, one Scroll, Scroll, two Scroll, Scroll, one Scroll, Scroll, two Scroll, Scroll, two Scroll, Scroll, two Scroll, Scroll, two Scroll, Five- c ­ size Block Mediem Medium Large Medium Large Medium Medium Medium Medium Medium b Pb (1σ) 3.7 (1.9) 7.1 (3.2) 4.9 (0.4) 6.0 (1.6) 12.8 (8.6) 6.9 (0.9) 4.7 (1.7) 16.0 (14.2) 34.3 (50.4) 80.2 (59.6) b (25.5) (13.2) (23.2) (11.3) (77.7) (13.3) (26.7) (28.7) (47.9) (19.6) Zr (1σ) 80.4 72.2 66.9 70.2 133.2 92.2 141.4 130.0 133.6 108.0 (70.1) b Y (1σ) 11.8 (6.8) 16.7 (5.9) 10.0 (2.8) 11.9 (1.3) 17.5 (6.1) 16.2 (3.0) 17.1 (5.8) 13.2 (3.1) 19.5 (6.5) 52.3 b Sr (1σ) 14 (3.4) 25 (12.6) 15 (4.4) 19 (5.5) 23 (5.4) 19 (2.4) 20 (2.6) 27 (7.2) 24 (5.2) 21 (2.4) b Rb (1σ) 24 (14.1) 27 (7.2) 25 (15.2) 22 (6.8) 42 (4.6) 40 (6.8) 43 (6.0) 40 (6.7) 37 (11.2) 42 (4.9) b Zn (1σ) 19.0 (4.6) 21.0 (7.5) 12.1 (3.9) 25.1 (2.7) 38.3 (12.9) 35.8 (8.3) 29.9 (10.7) 64.6 (41.5) 47.5 (14.3) 51.0 (26.1) b Cu (1σ) 11.4 (2.9) 19.2 (8.6) 14.0 (3.0) 15.0 (5.5) 50.2 (35.6) 27.4 (15.1) 17.4 (5.6) 72.6 (46.6) 32 (9.1) 21.6 (8.8) b (2660) (1080) (1050) (1280) (2660) (600) (1410) (880) (1640) (810) Fe (1σ) 8300 8600 8200 8900 15,800 11,800 12,400 12,500 11,000 11,100 b (150) (159) Mn (1σ) 161 (24) 231 142 (12) 159 (20) 217 (70) 179 (20) 182 (27) 204 (31) 201 (14) 456 b (239.6) Cr (1σ) 29.4 (16.5) 23.6 (13.0) 11.8 (2.3) 15.2 (8.2) 39.0 (18.3) 32.2 (15.2) 19.0 (5.0) 28.6 (4.2) 29.2 (7.0) 142.8 (189) (104) (135) (133) (146) (179) (91) (261) (238) (126) b (1σ) Ti 1000 970 800 870 1360 1370 1420 1460 1480 1330 b (220) (150) (140) (310) (120) (260) (2180) (1σ) Ca 6170 6350 6250 6190 (48) 6420 6090 (87) 6220 6350 6260 (58) 7860 (2440) (2380) (5280) (990) (1710) (1440) (1460) (1420) (2590) (1640) b K (1σ) 2860 4880 5530 2130 8080 6460 6580 7400 6090 6540 a (0.018) (0.016) (0.017) (0.013) (0.017) (0.017) (0.012) (0.016) (0.013) (0.012) MS (1σ) 0.045 0.030 0.023 0.025 0.055 0.057 0.051 0.067 0.049 0.068 Annex Hall (N2) west, upper structure U-shaped Extension (O1) L-shaped L-shaped Gallery (K2) upper structure L-shaped L-shaped Galley (K1) Building Western Western Eastern Gopura V (W) Western Western Gopura III (P) Gopura II (L) Eastern Hall (J) Gopura I (G) Mandapa (C) continued Khleang style period: the early 11th century the to mid-11th century) of the Khleang to style peri - ods: the mid-11th century to the end of the 11th century) 1 Table Stage 3rd (Late (Late 3rd 4th (End Uchida et al. Herit Sci (2017) 5:42 Page 8 of 15 blocks blocks headed naga headed naga headed naga headed naga headed naga headed naga Style of pedi - ends ment Scroll, two Scroll, Scroll, two Scroll, Five- Five- Five- Five- Five- Five- c ­ size Block Medium + large Large Large Large Large Large Large Medium + large Large Large Large Large b (142.7) Pb (1σ) 5.1 (1.3) 4.3 (2.3) 10.2 (8.4) 4.7 (2.0) 9.1 (4.1) 7.4 (2.7) 84.0 17.2 (19.4) 12.9 (4.8) 6.6 (1.8) 5.7 (1.1) 4.2 (1.3) b (32.1) (27.8) (67.1) (10.2) (10.2) (24.5) (33.3) (84.1) (75.5) (16.5) Zr (1σ) 76.5 (7.1) 89.1 80.1 114.1 66.0 68.5 83.6 93.9 63.9 (12.4) 140.7 123.8 86.5 (10.3) b Y (1σ) 12.5 (2.4) 11.8 (2.2) 12.2 (3.5) 15.3 (2.1) 14.7 (5.5) 18.3 12.7 (2.7) 12.6 (3.6) 30.0 (22.6) 19.4 (3.2) 12.5 (3.6) 19.0 (4.4) b Sr (1σ) 16 (2.5) 18 (7.0) 15 (4.3) 58 (32.8) 56 (23.4) 28 (13.7) 17 (1.8) 30 (12.5) 28 (15.8) 17 (0.9) 15 (4.4) 22 (7.1) b Rb (1σ) 25 (7.3) 27 (7.4) 29 (13.0) 32 (13.5) 24 (4.9) 18 (4.1) 27 (7.7) 33 (6.8) 20 (5.2) 33 (1.6) 28 (9.4) 32 (7.3) b Zn (1σ) 21.5 (10.8) 22.5 (10.3) 22.5 (9.6) 37.8 (16.8) 47.7(15.6) 37.5 (39.3) 41.2 (33.7) 82.1 (76.2) 66.0 (27.1) 32.6 (11.3) 21.4 (8.0) 34.4 (10.3) b (110.4) (115.5) Cu (1σ) 10.6 (6.2) 10.6 (1.6) 11.2 (3.7) 19.2 (9.9) 80.6 78.4 26.8 (13.4) 22.4 (12.2) 30.6 (27.5) 11.4 (3.7) 12.8 (3.9) 55.6 (39.2) b (1400) (2060) (2030) (2590) (1610) (690) (720) (1560) (900) (1000) (840) (1820) Fe (1σ) 8900 9200 10,500 9200 8400 7600 9300 11,100 8300 11,600 7049 11,300 b (122) (251) Mn (1σ) 159 (16) 169 (19) 210 (51) 175 (21) 176 (22) 190 (52) 322 244 (69) 336 215 (50) 153 (16) 210 (33) b Cr (1σ) 16.6 (4.5) 21.0 (11.7) 24.8 (10.5) 26.2 (7.5) 34.2 (15.9) 26.6 (11.0) 22.2 (7.7) 32.8 (4.3) 37.8 (23.7) 27.2 (12.7) 20.8 (15.2) 34.0 (7.6) (212) (340) (273) (395) (243) (164) (217) (199) (101) (211) (300) (91) b (1σ) Ti 1100 1140 1060 1270 1135 1140 1230 1360 1000 1180 1040 1310 b (210) (200) (160) (170) (140) (940) (460) (260) (360) (4380) (1σ) Ca 6240 6320 6160 (96) 6380 6250 6200 7280 7050 6460 6240 6110 (75) 9000 (1030) (3020) (2550) (2930) (1480) (4940) (2390) (4540) (2280) (930) (4790) (1730) b K (1σ) 2940 3950 4230 5820 7430 3750 4520 12,840 2800 4570 5040 6690 SI unit a − 3 (0.007) (0.016) (0.019) (0.012) (0.011) (0.011) (0.018) (0.016) (0.017) (0.015) (0.013) (0.018) MS (1σ) 0.036 0.042 0.032 0.020 0.019 0.022 0.034 0.033 10 0.027 0.037 0.024 0.036 Building (E) Building (F) Library (H1) Library (H2) Gopura (A) tuary (B) east west (Z1) (Z2) Building Western Western Eastern Gopura IV (T) Eastern Western Western South Central Sanc - Central Gallery (D) Gallery (D) Eastern Wall Eastern Wall Western Wall Wall Western Tower (Q) Tower continued - Magnetic susceptibility, ­ susceptibility, MS Magnetic huon to huon to Angkor style Wat periods: the mid-11th century to the end of the 12th century) Small: <50 cm in thickness and <50 cm in width, medium: <50 cm thickness thickness and 50–100 cm in width, large: >50 cm or >100 cm width (on average) ppm

1 Table Stage a b c 5th (Bap Uchida et al. Herit Sci (2017) 5:42 Page 9 of 15

planes. Similarly, sandstone blocks with square ends are remaining buildings, horizontally-elongated sandstone frequently observed in the Gopura V (W) and Gopura blocks, with high width/thickness ratios and primarily IV (T), and almost half of them have vertical bedding horizontal bedding planes, were used. planes. In contrast, the large sandstone blocks used in the Central Sanctuary (B), South Gopura (A), Gallery Pediment end styles (D), and Eastern Building (F) have mainly horizontal bed- Preah Vihear monument building pediment ends have ding planes. Sandstone blocks with face bedding are also two styles, based on their terminations (Fig. 4). One style observed in the South Gopura (A) and Gallery (D). In the of a pediment ends in scrolls. Such pediments also are

Fig. 4 Images showing pediment end styles at the Preah Vihear monument. a A pediment ending in scrolls made from one block [Gopura III (P)], (b) a pediment ending in scrolls made from two blocks [Gopura II (L)], (c) a pediment ending in scrolls made from two blocks [Western L-shaped Gallery (K2)], (d) a mortise of a pediment ending in scrolls made from two blocks [Western L-shaped Gallery (K2)], (e) a stone block with a tenon that fell from a pediment ending in scrolls made from two blocks [Western L-shaped Gallery (K2)], and (f) a pediment ending in fve-headed nagas [Gallery (D)] Uchida et al. Herit Sci (2017) 5:42 Page 10 of 15

observed in , , and of the fne to medium grain size, and magnetic susceptibilities −3 −3 early Angkor period (the end of the 9th century to the of 0.016–0.086 × 10 SI units (0.040 × 10 SI units on mid-10th century). Te other style ends in fve-headed average). Te Phu Phan Formation is white, with medium nagas (Fig. 4f). Tese pediments are observed in a wide to coarse grain size, and magnetic susceptibilities of less −3 −3 range of periods, from the Banteay Srei style period than 0.030 × 10 SI units (0.008 × 10 SI units on aver- to the style period in the middle to late Ang- age). Magnetic susceptibilities are highest for the Sao kor period (the mid-10th century to the early 13th cen- Khua Formation and lowest for the Phu Phan Formation, tury). Te scroll–style pediment ends can be subdivided with the Preah Vihear Formation magnetic susceptibili- into pediments that end in scrolls made from one block ties falling in the middle [1]. (Fig. 4a) and those that end in scrolls made from two Te sandstone used in the Preah Vihear monument blocks (Fig. 4b, c, e), yielding three distinct pediment end is mainly yellowish-brown (Fig. 3), and is medium to styles. Te pediments ending in scrolls made from two coarse grained. All the sandstone blocks of the Preah blocks are likely to be of a later style because they are not Vihear monument have magnetic susceptibility ranging −3 found in relatively older monuments such as Preah Ko, from 0.011 to 0.068 × 10 SI units, which is consistent Koh Ker and Banteay Srei. Te Annex Halls (N1 andN2), with their supply from the Preah Vihear Formation. Tis U-shaped Extensions (O1 and O2), Gopura III (P), and accounts for the abundant ancient sandstone quarries Gopura V (W) have pediments that end in scrolls made widely distributed around the Preah Vihear monument, from one block; while the Gopura II (L), Gopura I (G), especially in the eastern and western areas, along the Hall (J), Galleries II (K1 and K2), Western Building (E), causeway between the Gopura IV(T) and Gopura V(W) and Eastern Building (F) have pediments that end in (Fig. 3e, f). scrolls made from two blocks. Te South Gopura (A), Except for the Libraries (H1 and H2) had higher Sr Mandapa (C), Gallery (D), Libraries (H1 and H2), and contents of 58 and 56 ppm, respectively, the Sr contents Gopura IV (T) have pediments that end in fve-headed in sandstone blocks from the other buildings were less nagas. than 30 ppm. According to Uchida et al. [1], the Sr con- tent of the Preah Vihear Formation sandstone is typically Interpretation and discussion less than 40 ppm. Tis also supports the premise that the Origin of sandstone sandstone blocks used in the Preah Vihear monument Te sandstone used in the Preah Vihear monument is were quarried from the Preah Vihear Formation. siliceous sandstone (quartz arenite) and clearly difer- ent from the gray to yellowish-brown sandstone (felds- Construction chronological sequence pathic arenite) used in the Angkor monuments [17]. Tis Using results described above, we delineated fve con- siliceous sandstone of the early Cretaceous age is found struction stages for the Preah Vihear monument, as within the and Mt. Kulen regions (Fig. 1) described below (Table 1; Fig. 2). In particular, the Ti and [19]. In the Angkor monuments, red siliceous sandstone Rb contents, magnetic susceptibility, and size of the sand- blocks were uniquely used for Banteay Srei. For most of stone blocks, pediment end style, as well as the presence the rest of the Angkor monuments, the Red Terrain For- or absence of relief work on the tympana of the adjacent mation (called the Phu Kradung Formation in Tailand) buildings were important factors for determining these of the late Jurassic to the early Cretaceous supplied the stage divisions (Fig. 5). gray to yellowish-brown sandstone. Te Red Terrain For- We believe that the central part of the Western Annex mation is overlain conformably by the Upper Sandstone Hall (N2) was constructed frst (Fig. 6). Te sandstone Formation, which consists of siliceous sandstone of the blocks in the upper structure of the central part of the early Cretaceous age [19]. Te gray to yellowish-brown Western Annex Hall (N2) are markedly smaller than sandstone outcrops at the foot of the Khorat Plateau and those in the eastern and western parts of this West- Mt. Kulen, but was not used in the monuments on the ern Annex Hall (N2), as well as all other buildings in Khorat Plateau. In Tailand, the Upper Sandstone For- the monument. Teir size is similar to sandstone blocks mation is subdivided into three units, from bottom to used in the sanctuaries of and Phnom top, these are the Preah Vihear (Phra Wihan), Sao Khua, Bok of the Angkor area, constructed in the Bakheng and Phu Phan Formations. Tese formations are not style period (the end of the 9th century to the beginning homogeneous and vary in color. Te Preah Vihear For- of the 10th century). Te sandstone blocks used in the mation is mainly yellowish-brown, with fne to coarse platforms of Phnom Krom and also are thin grain size, and magnetic susceptibilities of less than (20–25 × 35–45 cm) compared with those used in their −3 −3 0.068 × 10 SI units (0.020 × 10 SI units on aver- sanctuaries [20]. Tis block style also occurs in the plat- age) [1]. Te Sao Khua Formation is primarily red, with form of the Western Annex Hall (N2). In addition, the Uchida et al. Herit Sci (2017) 5:42 Page 11 of 15

structure of the central part of the Western Annex Hall (N2) was constructed in the Bakheng style period (the end of 9th century to the beginning of the 10th century). Te platform of the central and western parts and the lower platform of the eastern part of the Western Annex Hall (N2) were likely constructed during the same period (Fig. 6), given that their sandstone blocks have similarly low magnetic susceptibilities. Given that the tympana of the U-shaped Extensions (O1 and O2) adjacent to the Annex Halls (N1 and N2) are undecorated, but the other tympana are decorated, we concluded that the U-shaped Extensions (O1 and O2) were constructed later than the Annex Halls (N1 and N2). Among these buildings, the Eastern Annex Hall (N1), Western U-shaped Extension (O2) and the east- ern part (the upper structure and the upper platform) of the Western Annex Hall (N2) were constructed dur- ing the second stage. Pediments that end in scrolls made Fig. 5 Plot showing the average Ti contents vs average magnetic from one block are found in all these buildings. Te susceptibilities for sandstone blocks used in construction of the Preah sandstone blocks used in these buildings are relatively Vihear monument. Data given in Table 1. Values are clearly character- rich in K, Ti, Fe, Zn, Rb, and Zr. Although the Eastern istic of diferent stages of construction U-shaped Extension (O1) has pediments that end in scrolls made from one block, its sandstone blocks have diferent chemical compositions and magnetic suscep- magnetic susceptibilities of the sandstone blocks in the tibilities from those of the Eastern Annex Hall (N1), upper structure of the central part of the Western Annex Western U-shaped Extension (O2), and the eastern part Hall (N2) are the lowest of any of the Preah Vihear monu- of the Western Annex Hall (N2). Terefore, the Eastern ment. Furthermore, 54% of the sandstone blocks of the U-shaped Extension (O1) likely belongs to the third stage upper structure of the central part of the Western Annex of construction. Te sandstone blocks in the upper struc- Hall (N2) have vertical bedding planes. Tis arrangement ture of the eastern part of the Western Annex Hall (N2) of blocks suggests that the central part of the Western have similar chemical compositions to those in the East- Annex Hall (N2) was constructed in or before the Ang- ern Annex Hall (N1) and Western U-shaped Extension kor Wat style period (before the end of the 12th century) (O2). Tis suggests that the upper structure of the east- [21]. Tus, the sandstone blocks and their arrangement ern part of the Western Annex Hall (N2) was extended in the upper structure of the central part of the Western while construction of the Eastern Annex Hall (N1) and Annex Hall (N2) are markedly diferent from those of the Western U-shaped Extension (O2) was undertaken. Te other parts of the Western Annex Hall (N2) and the other sandstone blocks in the upper structure of the west- buildings. Teir characteristics suggest that the upper ern part of the Western Annex Hall (N2) have similar

Fig. 6 Photograph of the southern face of the Western Annex Hall (N2) showing sections constructed during various stages. The central part (the platform and upper structure), the lower platform of the eastern part, and the platform of the western part were constructed frst (frst stage); the upper structure and upper platform of the eastern part followed (second stage); and fnally, the upper structure of the western part was con- structed (third stage) Uchida et al. Herit Sci (2017) 5:42 Page 12 of 15

chemical compositions and magnetic susceptibilities to Judging from the pediment end style, construction of those of the Eastern U-shaped Extension (O1). Tis sug- the Gopura I (G), Hall (J), Gopura II (L), and Eastern gests that the upper structure of the western part of the L-shaped Gallery (K1), and then Mandapa (C) may have Western Annex Hall (N2) was extended during the third followed the construction of the Gopura III (P). stage, clearly later than the eastern part (second stage). Te sandstone blocks of the Gopura II (L) are similar Given the similarity in style of the Eastern Annex in chemical compositions and magnetic susceptibilities Hall (N1) to the Khleang temple in the Angkor area, we to those of the Eastern L-shaped Gallery (K1), but difer believe that the second construction stage corresponds from those of the Western L-shaped Gallery (K2). Tis to the Khleang style period (the mid-10th century to the suggests that the Eastern L-shaped Gallery (K1) was con- mid-11th century). Te Eastern Annex Hall (N1) has an structed at a diferent time to the Western L-shaped Gal- inscription (K381), which describes an event that took lery (K2) (during the second to third stages). Te style of place in AD 1024 [10] or AD 1026 [12]. Tis suggests the pediment ends suggests that the Western L-shaped that the Eastern Annex Hall (N1) and Western U-shaped Gallery (K2) was constructed after the Gopura III (P). Extension (O2) were completed around AD 1024 or AD However, the construction sequence inferred from the 1026. style of the pediment ends contradicts that derived from Te Gopura V (W) was also likely constructed during the chemical compositions and magnetic susceptibilities the third stage, because its sandstone blocks have simi- of their sandstone blocks. lar chemical compositions and magnetic susceptibilities Te inscription (K380) on the door frame of the to those of the Eastern U-shaped Extension (O1), and it Gopura II (L) consists of three sets of texts written in has pediments that end in scrolls made from one block. AD 1037–1038, AD 1038, and AD 1049, which describes Te sandstone blocks used in the upper structure of the events from AD 1018 [10–12]. Tis suggests that the Western L-shaped Gallery (K2) are also similar in chemi- Gopura II (L) was constructed at the end of the Khleang cal compositions and magnetic susceptibilities to those style period (the mid-11th century). Terefore, the of the Eastern U-shaped Extension (O1), suggesting that buildings in the fourth stage are estimated to have been the upper structure of the Western L-shaped Gallery (K2) constructed from the end of the Khleang style to the Bap- was constructed in this third stage. However, the West- huon style (the mid-11th century to the end of 11th cen- ern L-shaped Gallery (K2) has pediments that end in tury) periods. scrolls made from two blocks, which are diferent from Te remaining buildings at the site belong to the ffth those in the Eastern U-shaped Extension (O1). Given stage. Te sandstone blocks of these buildings have lower the chemical compositions and magnetic susceptibilities magnetic susceptibilities than those belonging to the sec- of its constituent blocks, we consider the possibility that ond and fourth stages, and their chemical contents of K, the platform of the Western L-shaped Gallery (K2) was Ti, Fe, Zn, Rb, and Zr fall between those of the second constructed using the same sandstone blocks as those and fourth stages, and those of the third stage (Fig. 5). used in second-stage buildings. Tis is supported by the Te Western and Eastern Buildings (E and F) have ped- fact that the sandstone blocks of the third stage have dis- iments that end in scrolls made from two blocks; thus, we tinctly lower K, Ti, Fe, Zn, Rb, and Zr contents and mag- infer their construction slightly before the Central Sanc- netic susceptibilities than those of the second stage. tuary (B), Gallery (D), South Gopura (A), Gopura IV (T), We infer that the Gopura III (P) was constructed after and Libraries (H1 and H2), which all have pediments that the U-shaped Extensions (O1 and O2) because reliefs end in fve-headed nagas. We believe that the Gopura IV were carved on the tympana of the U-shaped Exten- (T) was constructed frst among these buildings, because sions (O1 and O2), but were left unfnished on those of its sandstone blocks have square ends and almost half of the Gopura III (P) adjacent to the U-shaped Extensions them have vertical bedding planes, which are frequently (O1 and O2). In addition to the Gopura III (P), Gopura seen in the platform. II (L), Hall (J), Gopura I (G), Mandapa (C), and Eastern In contrast to the other buildings, the sandstone blocks L-shaped Gallery (K1) were constructed in the fourth of the Libraries (H1 and H2) are uniformly high in Sr and stage, characterized by sandstone blocks with relatively have similar magnetic susceptibilities to each other. Tis high K, Ti, Fe, Zn, Rb, and Zr contents and magnetic suggests that the Libraries (H1 and H2) were constructed susceptibilities. Medium-sized sandstone blocks were at the same time. Given the site layout, we infer that the used in all of these buildings, except for the Gopura III Libraries (H1 and H2) were constructed after the Gopura (P). Te Gopura III (P) has pediments that end in scrolls I (G), Hall (J), Gopura II (L), and Galleries (K1 and K2). made from one block, while the Mandapa (C) has pedi- Tis is supported by the fact that the Libraries (H1 and ments that end in fve-headed nagas. Te other buildings H2) have pediments that end in fve-headed nagas, have pediments that end in scrolls made from two blocks. whereas the buildings surrounding the Libraries (H1 and Uchida et al. Herit Sci (2017) 5:42 Page 13 of 15

H2) have pediments that end in scrolls made from two Parmentier [9] and Sahai [12] are outlined in Table 2. blocks. Decoration also is more elaborate on the Librar- Parmentier [9] used an architectural viewpoint, while ies (H1 and H2), as well as on the Mandapa (C) and Hall Sahai [8] used inscriptions to establish a sequence. Te (J), compared with other buildings in this stage. sequence obtained in this study difers considerably Te large sandstone blocks of the South Gopura (A), from those obtained by both Parmentier [9] and Sahai Central Sanctuary (B), Gallery (D), and Tower (Q) have [12]. Based on its sandstone block characteristics, we similar chemical compositions and magnetic suscepti- concluded that the Western Annex Hall (N2) is the old- bilities. In addition, these buildings, except for the Tower est edifce in the Preah Vihear monument. Tis is not (Q), have pediments that end in fve-headed nagas. Given consistent with the construction sequences proposed by these facts, we infer that these buildings were constructed Parmentier [9] or Sahai [12]. Tey did not recognized at nearly the same time. Because the Tower (Q) has no that the Western Annex Hall (N2) was the oldest build- decoration and is unfnished, it may have been the last ing in the construction sequence of the Preah Vihear construction undertaken in the Preah Vihear monument. monument. However, we support their inference that Because large sandstone blocks were used, with bedding the Eastern Annex Hall (N1) and U-shaped Extensions planes that are mainly horizontal [21], the South Gopura (O1 and O2) were constructed in the late Khleang style. (A), Central Sanctuary (B), and Gallery (D) are consist- Both authors considered that the Mandapa (C), Gopura ent with the style period (the end of the 11th I (G), Hall (J), and Gopura II (L) were constructed before century to the end of the 12th century). In contrast, the the Annex Halls (N1 and N2) and U-shaped Extensions Eastern Building (F), Western Building (E), Gopura IV (O1 and O2). Te South Gopura (A) and Gallery (D) also (T), and Libraries (H1 and H1) belong to the Baphuon were inferred to be older than the Annex Halls (N1 and style period (the mid-11th century to the end of the 11th N2) and U-shaped Extensions (O1 and O2) in their stud- century), and were constructed before the South Gopura ies, being diferent from this study. Meanwhile, all stud- (A), Central Sanctuary (B), and Gallery (D), based on ies support that the Gopura III (P) was constructed later their sandstone characteristics. than the Annex Halls (N1 and N2) and U-shaped Exten- For comparison, the construction sequences for sions (O1 and O2). We concluded that the Gopura III (P), the Preah Vihear monument previously inferred by Gopura II (L), Hall (J), Gopura I (G), and Mandapa (C)

Table 2 Comparison of the constructions sequences for the Preah Vihear monument proposed by Parmantier [9], Sahai [12] and this study Uchida et al. Herit Sci (2017) 5:42 Page 14 of 15

were constructed during the same period (in late Khleang Tird stage (the late Khleang style period:the early style to the Baphuon style (the beginning of the 11th cen- 11th century to the mid-11th century): construction of tury to the end of the 11th century) based on their simi- the upper structure of the western part of the Western lar sandstone block chemical compositions and magnetic Annex Hall (N2), Eastern U-shaped Extension (O1), the susceptibilities. upper structure of the Western L-shaped Gallery (K2), All three studies agree that the Central Sanctuary (B) and Gopura V (W) took place. All buildings, except for was constructed in the fnal stage. However, Parmen- the Western L-shaped Gallery (K2) constructed during tier [9] and Sahai [12] considered the South Gopura (A) the second and third stages, have pediments that end in and Gallery (D) surrounding the Central Sanctuary (B) scrolls made from one block. Te sandstone blocks in the to have been constructed during the same period as the third stage are relatively depleted in K, Ti, Fe, Zn, Rb, and Mandapa (C). However, we found their sandstone block Zr. Tey also have low magnetic susceptibilities. characteristics to be distinctly diferent. Large sandstone Fourth stage (the end of the Khleang style period to the blocks were used in the South Gopura (A) and part of Baphuon style period:the mid-11th century to the end the Gallery (D) as well as in the Central Sanctuary (B), in of the 11th century): construction of the Gopura III (P), contrast to the Mandapa (C). In addition, the sandstone Eastern L-shaped Gallery (K1), Gopura II (L) (around blocks of the South Gopura (A) and Gallery (D) are dif- AD 1038 or AD 1049), Hall (J), Gopura I (G), and Man- ferent in chemical compositions and magnetic suscep- dapa (C) took place. Te sandstone blocks used for these tibilities from those of the Mandapa (C), but similar to buildings are characterized by high magnetic susceptibil- those of the Central Sanctuary (B). Given these facts, it ities and high K, Ti, Fe, Zn, Rb, and Zr contents. Te ped- is difcult to accept the construction sequences for these iment terminations changed from scrolls to fve-headed buildings proposed by either Parmentier [9] or Sahai [12]. nagas. Fifth stage (the Baphuon style period to the Angkor Conclusions Wat style period:the mid-11th century to the end of the Using sandstone block chemical and magnetic charac- 12th century): construction of the Western Building (E), teristics, as well as stone arrangement and decoration, Eastern Building (F), Gopura IV (T), Libraries (H1 and a construction sequence for the buildings in the Preah H2), South Gopura (A), Central Sanctuary (B), Gallery Vihear monument was established comprising fve stages. (D), Walls (Z1 and Z2) near Libraries, and Tower (Q) Te buildings and their distinctive stone characteristics took place. Fifth-stage buildings are characterized by are outlined below in order of their construction: large sandstone blocks and pediments with fve-headed First stage (the Bakheng style period:the end of the 9th nagas. century to the beginning of the 10th century): initial con- Te construction sequence described above is almost struction of the upper structure of the central part and in harmony with the change of pediment end styles from platform of the Western Annex Hall (N2) took place to pediments ending in scrolls made from one block, to form the oldest edifce in the Preah Vihear monument. pediments ending in scrolls made from two blocks, and Te sandstone blocks in this stage are characterized by fnally to pediments ending in fve-headed nagas. In addi- low magnetic susceptibilities, small block size, with a tion, the construction sequence suggests that the sand- high percentage of vertical bedding planes. Te stone stone block size increased over time. block characteristics of the Western Annex Hall (N2) Authors’ contributions are completely diferent from the other buildings in the EU and AM conceived and coordinated this research. All authors conducted Preah Vihear monument. Previous works by Parmantier the feld work. EU and AM interpreted data. EU drafted the manuscript and AM and IS revised it critically. All authors read and approved the fnal manuscript. [9] and Sahai [12] did not recognized that this building was the oldest one in the construction sequence of the Author details Preah Vihear monument. 1 Department of Resources and Environmental Engineering, Waseda Univer- sity, Ohkubo 3‑4‑1, Shinjuku‑ku, Tokyo 169‑8555, Japan. 2 Department of Archi- Second stage (the middle Khleang style period:the early tecture, Meijo University, Shiogamaguchi 1‑501, Tenpaku, Nagoya 468‑8502, 11th century): ongoing construction of the upper struc- Japan. 3 World Heritage Studies, The University of Tsukuba, Kasuga 1‑8‑3, ture of the eastern part of the Western Annex Hall (N2), Tsukuba, Ibaraki 305‑0821, Japan. Eastern Annex Hall (N1) (around AD 1024 or AD 1026), Acknowledgements Western U-shaped Extension (O2), and the platform This project was conducted with the co-operation of Ministry of Culture and of the Western L-shaped Gallery (K2) took place. Te Fine Arts and the National Authority for Preah Vihear, Cambodia. We would like to thank members of the Japanese Government Team for Safeguarding sandstone blocks used in this second stage are relatively Angkor for their help during our research. We appreciate the useful and con- enriched in K, Ti, Fe, Zn, Rb, and Zr and have high mag- structive comments received from three anonymous reviewers. netic susceptibilities. Uchida et al. Herit Sci (2017) 5:42 Page 15 of 15

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