RESEARCH ARTICLE
First Direct Dating for the Construction and
Modification of the Baphuon Temple
Mountain in Angkor, Cambodia
Stéphanie Leroy1*, Mitch Hendrickson2, Emmanuelle Delqué-Kolic3, Enrique Vega1,
Philippe Dillmann1
1 Archaeomaterials and Alteration Prediction Laboratory (LAPA), LMC-IRAMAT UMR5060/NIMBE
UMR3685, Centre National de la Recherche Scientifique, CEA Saclay, Gif/Yvette, France, 2 Department of
Anthropology, University of Illinois at Chicago, Chicago, Illinois, United States of America, 3 Measurement of
Carbon 14 Laboratory (LMC14), National Platform, LSCE UMR8212, Centre National de la Recherche
Scientifique, CEA Saclay, Gif/Yvette, France
* stephanie.leroy@cea.fr
Abstract
OPEN ACCESS
Citation: Leroy S, Hendrickson M, Delqué-Kolic E,
Architecture represents key evidence of dynastic practice and change in the archaeological
Vega E, Dillmann P (2015) First Direct Dating for the world. Chronologies for many important buildings and sequences, including the iconic tem-
Construction and Modification of the Baphuon Temple ples of medieval Angkor in Cambodia, are based solely on indirect associations from
Mountain in Angkor, Cambodia. PLoS ONE 10(11):
inscriptions and architectural styles. The Baphuon temple, one of the last major buildings in
e0141052. doi:10.1371/journal.pone.0141052
Angkor without textual or scientifically-derived chronological evidence, is crucial both for the
Editor: Siân E Halcrow, University of Otago, NEW
context and date of its construction and the period when its western façade was modified
ZEALAND
into a unique, gigantic Reclining Buddha. Its construction was part of a major dynastic
Received: May 19, 2015
change and florescence of the Hindu-Mahayana Buddhist state and the modification is the
Accepted: October 1, 2015 key evidence of Theravada Buddhist power after Angkor's decline in the 15th century. Using
Published: November 4, 2015 a newly-developed approach based on AMS radiocarbon dating to directly date four iron
Copyright: © 2015 Leroy et al. This is an open
crampons integrated into the structure we present the first direct evidence for the history of
access article distributed under the terms of the the Baphuon. Comprehensive study of ferrous elements shows that both construction and
Creative Commons Attribution License, which permits modification were critically earlier than expected. The Baphuon can now be considered as
unrestricted use, distribution, and reproduction in any
the major temple associated with the imperial reformations and territorial consolidation of
medium, provided the original author and source are
credited. Suryavarman I (1010–1050 AD) for whom no previous building to legitimize his reign could
be identified. The Theravada Buddhist modification is a hundred years prior to the conven-
Data Availability Statement: All relevant data are
within the paper. tional 16th century estimation and is not associated with renewed use of Angkor. Instead it
relates to the enigmatic Ayutthayan occupation of Angkor in the 1430s and 40s during a
Funding: Funding for this project was provided by
the French National Research Agency (IRANGKOR major period of climatic instability. Accurately dating iron with relatively low carbon content
project, ANR-14-CE31-0007), http://www.agence- is a decisive step to test long-standing assumptions about architectural histories and politi-
nationale-recherche.fr/?Project=ANR-14-CE31-0007 cal processes for states that incorporated iron into buildings (e.g., Ancient Greece, medieval
(received the funding: SL) and the Australian
India). Furthermore, this new approach has the potential to revise chronologies related to
Research Council Discovery Project (DP0987878),
https://researchdata.ands.org.au/industries-angkor- iron consumption practices since the origins of ferrous metallurgy three millennia ago.
material-centuries-ce/65492 (received the funding:
MH). The funders had no role in study design, data
collection and analysis, decision to publish, or
preparation of the manuscript.
PLOS ONE | DOI:10.1371/journal.pone.0141052 November 4, 2015 1 / 13
First Direct Dating for the Baphuon Temple
Competing Interests: The authors have declared Introduction
that no competing interests exist.
Monuments are direct symbols of pre-modern state’s politico-economic power and capability
to control resources. The ability to harness labour and materials on such large scales is a prod-
uct of specific spatio-temporal contexts (history, environment) yet the majority of buildings
are dated indirectly via inscriptions, historical references or architectural styles [1,2]. The 9th to
13th centuries AD temples at the UNESCO World Heritage Site of Angkor in northern Cambo-
dia epitomize this process as the architectural phases of hundreds of buildings are derived from
Sanskrit or Khmer language inscriptions carved onto the walls or on nearby dedicatory steles
of a few ‘type’ sites [3]. Establishing direct techniques to verify construction episodes is compli-
cated by the lack of datable remains (e.g., wood) from secure contexts. Iron crampons are the
most consistently available material both in Angkorian and pre-modern architectural tradi-
tions however previous attempts at radiocarbon dating were fraught by methodological diffi-
culties [4]. Application of a newly developed AMS radiocarbon approach combining
radiocarbon dating, metallographic and archaeometric analyses of iron elements for the
Baphuon temple, one of the last undated monuments in Angkor, provides the first evidence of
its construction and subsequent modification. This new history is integrated within the dynam-
ics of 11th century Khmer kingship as well as the recently published climatic sequence, which
has remained focused solely on questions of Angkor’s demise in the late 14th and 15th centuries
[5,6].
The Baphuon, situated next to the royal palace inside the late 12th century enclosure of Ang-
kor Thom (Fig 1), is the only temple mountain associated with the 11th century [7], an era of
bureaucratic consolidation that enabled Khmer territorial dominance over the next 200 years.
Equally significant is the later modification of its western façade into the 70m long Reclining
Buddha, the presence of which depicts the state-level transition from Mahayana to Theravada
Buddhism and capacity to undertake major projects after Angkor’s peak in the 13th century.
Assessing when the construction and modification events occurred is vital not only to the
Baphuon’s individual history but also understanding the dynamics between monumental
architecture, political processes and the shifting climatic record in medieval Southeast Asia [6].
Unlike temple mountains in Angkor such as Pre Rup, Ta Keo, and Bayon, the Baphuon
chronology is complicated by the absence of related inscriptions and scholars unable to accu-
rately identify it with buildings described in 11th century texts recovered elsewhere [11,12].
Theories oscillated between the reigns of Jayavarman V (968–1000 AD), Suryavarman I (1010–
1050 AD) and Udayadityavarman II (1050–1065 AD) however standard attribution in aca-
demic publications and guidebooks favour the last of these rulers. A critical issue is whether
this represents consecration rather than construction particularly as Suryavarman I is not asso-
ciated with any temple in Angkor and the short time-span of Udayadityavarman II’s reign to
complete this project during a period of episodic droughts beginning around 1050 AD [6]. The
Reclining Buddha modification similarly lacks any primary textual record and is based on the
terminal use of Angkor by Theravada Khmer king(s) in the mid to late 16th century [13], subse-
quent architectural inference to the late 15th to 16th century [7], and the presence of distinctive
flat chisel marks on buildings and statuary related to the late 15th to 16th centuries [14]. As
other Theravada architectural renovations in Angkor such as the seated Buddha on Phnom
Bakheng are now demolished [15], dating the Reclining Buddha will allow identification of
whether the last major architectural modifications in Angkor occurred earlier or later in its
decline from the 14th to the 16th centuries.
Beyond dating rarely preserved wooden supports [16], iron crampons fixed between inter-
nal sandstone blocks remain the most consistent in situ artefact to determine the construction
date or modification phases in Angkorian temples. Anastylosis of the Baphuon [10] recovered
PLOS ONE | DOI:10.1371/journal.pone.0141052 November 4, 2015 2 / 13
First Direct Dating for the Baphuon Temple
Fig 1. The Baphuon temple. (A) Location within the 12th c walled enclosure of Angkor Thom (adapted from Angkor GIS map data of Pottier [8] and Evans [9]
for illustrative purposes only). (B) Details of the eastern façade. (C) Plan showing location of the Reclining Buddha outlined in red (plan of Baphuon similar but
not identical to the original image from Royère [10] and is for illustrative purposes only). (D) Details of the modification of the western façade.
doi:10.1371/journal.pone.0141052.g001
nine iron crampons, including eight bow-tie crampons arranged in pairs from two separate
foundation levels associated with the crowning walls from the initial construction phase and
one u-shaped crampon behind the head of the Reclining Buddha modification (Fig 2). We
therefore investigated the nine crampons and tools and used a new approach based on radio-
carbon dating to directly date metal itself [4]. The basic idea for dating ferrous alloys by radio-
carbon is that the carbon contained in the steely zones of the ancient metal (actually an iron-
carbon alloy) comes from the charcoal used during ore smelting. During the manufacture of
the alloy, the carbon from charcoal and from the CO resulting from its combustion is incorpo-
rated by diffusion into the metal. The final metallographic form of the steel contains pearlite: a
mix of ferrite (containing less than 0.02 wt% of C) and cementite (Fe3C). If the metal contains
more than 0.8 wt% of carbon, zones of pure cementite can be found. Lastly, when the carbon
content is more than 2 wt%, the metal is considered as cast iron and can contain graphite in
addition to the former compounds. Presence of carbon in the structure is therefore not relative
to single fragments of charcoal but to carbon-containing compounds obtained after chemical
PLOS ONE | DOI:10.1371/journal.pone.0141052 November 4, 2015 3 / 13
First Direct Dating for the Baphuon Temple
Fig 2. Location of bow-tie crampons from the original structure (BPN-30001, BPN-30002, BPN-30006) and the u-shaped crampon behind the head
of the Reclining Buddha modification (BPN-30009) that could have been dated. Section of Baphuon is similar but not identical to the original image from
Royère [17] and is for illustrative purposes only.
doi:10.1371/journal.pone.0141052.g002
reaction with the carbon of the initial charcoal. For the bloomery process, the carbon contents
heterogeneously distributed within the metallic matrix are generally relatively low (<2 wt% of
C). This very slight carbon content can be extracted and its isotopic ratio determined. A reliable
radiocarbon date can be determined as long as the nature of the material being analyzed is pre-
viously documented (i.e., not recycled) [4]. We hence provide a consistent and incontrovertible
evidence of the production date of these crampons.
Materials and Methods
The nine crampons (named BPN-30001 to BPN-30009) are housed at the Siem Reap Center
(Cambodia) of the École Française d’Extrême-Orient. All necessary permits for exportation
and for the described study which complied with all relevant regulations were obtained from
the Authority for the Protection and Safeguarding of Angkor Region Authority (APSARA) by
the EFEO.
Preparation of iron samples
Because of the heterogeneous nature of the ancient metal structure, the samples were initially
subjected to the preparation and the measurement procedures recently developed to obtain
reliable AMS 14C dates from iron supports in French medieval cathedrals [4]. Detailed metallo-
graphic investigation of the matrix [18] was followed by analysis of several hundred of Slag
inclusion (SI) [19] to study the microstructure of the metal and detect any potential recycling
case after the initial smelting process [20], a prerequisite for reliable 14C dating [4].
PLOS ONE | DOI:10.1371/journal.pone.0141052 November 4, 2015 4 / 13
First Direct Dating for the Baphuon Temple
Specimens of about 2 cm3 taken at each end of these iron were therefore cross-sectioned to
expose both the metallic matrix and the SI entrapped in the metal. Each iron cross-section was
polished using SiC abrasive paper (grades 80–4000). Final polishing was performed using
Struers diamond polishing medium 9, 3 and 1 μm. The cross-sections were then cleaned by
two ethanol washes in an ultrasonic bath to suppress any carbon contamination.
SI found within most archaeological bloomery iron artefacts are remainders of slag created
during the smelting and smithing processes. Their compositional analysis therefore provides
pertinent information about the manufacturing of the object. Certain major compounds of the
ore that are not reduced during smelting (noted NRC for Non Reduced Compounds: mainly
Al2O3, SiO2, K2O, CaO and MgO) have in most cases a constant ratio in the SI of each artefact.
The signature of a system or a smelting operation with the same ore, charcoal, fluxes and fur-
nace lining can therefore be identified. In a case of recycling (iron artefacts containing separate
pieces, welded or forged together), different constant ratios can be detected in their SI and,
therefore, various signatures can be identified within the sample [20]. Prior to sampling for
radiocarbon measurements, we performed the major element composition of ideally several
hundred SI per sample to be statistically representative of the artefact. SI composition of pol-
ished samples was studied according to the protocol detailed in [19] to enable investigation of
the entire sample surface of the sample. Taking into account all detectable NRCs, the raw SI
NRC data were then log-ratio transformed to obtain subcompositional values [19,21]. We
finally used statistical methods (Principal Component Analysis (PCA) and cluster analysis) to
discriminate SIs derived from smelting slag from all others and identify one chemical signature
for each artefact [21].
The metallographic study of the matrix alloy reveals the distribution of the carbon content
and therefore provides the solution of targeting the most carburized areas in the sample as
detailed in [4]. Metallographic etchings were done on the polished cross-sections using Nital
4% that were finally washed with de-ionized water, followed by ethanol and then dried in an
oven at 80°C. The sample was washed with de-ionized water, followed by ethanol and then
dried in an oven at 80°C. Samples were finally observed under an OLYMPUS light microscope
(BX51 model) under reflected light to visualize the distribution of carbon within the metal as
well as the potential welding lines.
Carbon extraction
After preparation, we collected samples in the highest carburized zones with CoB (Cobalt
Boron) coated drills of several millimeter diameters (Ø2 mm or Ø3.5 mm). We sampled the
weight required (a few hundred milligrams) to obtain up to an ideal of 1 mg of carbon [4]. The
resulting samples were combusted to CO2 according to the newly adapted combustion
approach [4]. The CO2 samples were finally graphitized automatically at the LMC14 laboratory
according to the protocol described by Cottereau et al. [22].
AMS measurements and calibration
The 14C measurements were performed with ARTEMIS, the AMS facility installed in Saclay
(France) [22]. Calendar age ranges were calculated using Oxcal 4.2.4 [23] with the SHCal04 cal-
ibration [24] curve by applying a small offset of -21 +/-6 yrs as proposed by Hua et al. [25], the
atmospheric 14C over tropical regions in Southeast Asia being a result of Northern and South-
ern Hemisphere air-masses mixing via the monsoon systems. For all the samples, we used an
average value of the 14C contents measured for 14C free charcoal as the background value [4].
The radiocarbon ages measured on the same crampon, being related to the same event [4],
PLOS ONE | DOI:10.1371/journal.pone.0141052 November 4, 2015 5 / 13
First Direct Dating for the Baphuon Temple
were combined using the R_Combine function implemented within the Oxcal program, ver-
sion 4.2.4 [23] to calculate a combined age density [26] representative of the crampon.
Results
Based on the carbon content distribution within the metal, four specimens coming from the
first and third stages of the temple (BPN-30001, BPN-30002, BPN-30006), and the head of the
Reclining Buddha (BPN-30009) were sufficiently carburized to be targeted and collected for
the 14C measurements (Figs 2 and 3). No evidence of cementation that could modify the initial
date [27] could be observed. Welding lines were visible but investigations of the SI did not
reveal different chemical signatures indicative of the use of metal pieces from different reduc-
tion systems for the manufacture of the crampon, and therefore potentially made of recycled
scrap iron (i.e., older iron) (see example in Fig 4). These observations strongly reduce risks of
metal recycling case but do not eliminate potential reuse of the ancient clamps. For three cram-
pons (BPN-30001, BPN-30002 and BPN-30009), it was possible to collect two sub-samples and
therefore obtain two radiocarbon ages per specimen that were combined to refine the cali-
brated age.
Considering the long-standing issue of the old wood effect in radiocarbon dating, the inte-
gration of anthracology analysis of material recovered from furnaces would have been very use-
ful to broaden our knowledge about the preparation of charcoal. Unfortunately, the
development of anthracology and comparative databases of local wood and potential fuels is
extremely limited in Southeast Asia and information regarding the identification of the type of
wood used for charcoal preparation type is not yet available. Nevertheless, the large scale pro-
duction of iron, ceramics and buildings (settlement, temples) during this period [28] does not
support the long-term curation of heartwood for ironmaking (i.e., leading to old wood). Obser-
vations from many contemporary rural communities in South East Asia (Thailand and Burma)
highlight the logical economic/practical issues of wood selection for fuel, specifically that char-
coal is rarely made from big pieces of wood due to the problems of controlling the charring
process. Smaller trunks or branches are preferred as they obviate a lot of cutting and shaping
while old wood in good condition, which has a high market value and was not cut up or use it
for charcoal anyway. Furthermore, rotten wood cannot be used to efficiently make charcoal
(Janice Stargardt, personal communication, August 19, 2015). Moreover, note that for 14C dat-
ing of iron, we do not measure single fragments of charcoal but bulked carbon incorporated in
the metallic structure that derives from a mixing of the totality of the charcoal used as fuel dur-
ing the reduction operation and through the CO gas produced by its combustion during the
process. Unlike 14C dating of fragments of charcoal, this process would tend to drastically min-
imize the old wood effect if indeed long-lived trees were used in the production of charcoal, by
averaging the contribution of all the charcoal pieces put in the furnace. In view of all these
observations, we are therefore confident that the dates produced by this approach represent the
smelting dates of the original iron.
The 14C ages of all samples dated are listed in Table 1 and the calibrated temporal densities
with a 95.4% probability ranges are shown in Fig 5. The two radiocarbon dates for BPN-30001
(BPN-30001(1) and BPN-30001(2)) and BPN-30009 (BPN-30009(1) and BPN-30009(2)) are
fully coherent and can be combined with >95% probability to calculate a combined age density
strongly representative of each crampon. The combined dates are respectively 984–1028 calAD
at 95.4% probability ranges for BPN-30001 (with Chi-Squared test statistic of 0.6 v. 3.8 for
df = 1) and 1416–1452 calAD at 95.4% probability ranges for BPN-30009 (with Chi-Squared
test statistic of 0.1 v. 3.8 for df = 1). The two results obtained for BPN-30002 show some over-
lap but the disparity between the slightly older BPN-30002(1) (868–993 calAD, 95.4%) and
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First Direct Dating for the Baphuon Temple
Fig 3. Documentation of the dated specimens. Sampled parts within each crampon are shown in white. Schematic drawings of the microscopic
metallographic observation on the cross-section after Nital etching enlighten the distribution of the carbon content within the metal. The black marks within
the metal of the most carburized samples, selected for the radiocarbon measurements, indicate the fingerprint of the drill samples. 2 dates were obtained for
each crampon BPN-30001 and BPN-30002. Both samples BPN-30009(1) and BPN-30009(2) from BPN-30009 could be dated therefore providing 2 dates for
the crampon.
doi:10.1371/journal.pone.0141052.g003
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First Direct Dating for the Baphuon Temple
Fig 4. Treatment of SI measurements for BPN-30009 (BPN-30009(1) and BPN-30009(2)) for which numerous welding lines were identified. (A)
Localisation of the hyperspectral maps performed on representative zones of each artefact BPN-30009(1) and BPN-30009(2). (B) (left) BPN-30009(1) and
BPN-30009(2) SI subcompositional ratios (noted Xij NRC) projected onto the first two PC axes. The PCA conducted on the standardized Xij NRC (in this case,
the only detectable NRCs are Al2O3, SiO2, MgO, CaO) and a hierarchical cluster analysis [21] reveals 6 groups (one color per group). Comparing group
projections and loading structure (right), “black and grey” group is identified as smelting slag; red group seems to be derived from or contaminated with silica
flux; green, blue, brown and orange groups derived from or contaminated with fuel ash. For more information [21]. (C) (left) X-ray map of an analyzed zone at
O Kαline and spotting of the contaminated SI identify by the statistical analysis. (Right) The SI colored in green are representing SI from green group. It is not
possible to identify various groups within the group identified as smelting slag evidencing that the Xij NRC and therefore the chemical signatures are
comparable for the different parts of BPN-30009(1) and BPN-30009(2) and between them. No case of recycling was detected for BPN-30009.
doi:10.1371/journal.pone.0141052.g004
slightly younger BPN-30002(2) (991–1050 calAD 52.2%; 1078–1145 calAD, 43.2%) does not
allow calculation of a combined age with the same level of confidence. Because both measure-
ments are strongly supposed to equally date the same event (production of the crampon with
the same fuel) and therefore to be coherent, both effects in the calendar distribution are likely
to be explained by the presence of two plateaux on the calibration curve (around 1000 BP and
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First Direct Dating for the Baphuon Temple
Table 1. Radiocarbon dating results for the crampons from the original structure (BPN-30001, BPN-30002, BPN-30006) and Reclining Buddha
modification (BPN-30009).
Sample name Lab.ID Extracted carbon content δ13C (‰) pMC Radiocarbon age Calibrated age (calAD)
acA (mg) (BP, 1 σ) (95.4%)
BPN-30009(1) 32535 1.30 -20.9 94.25± 0.36 476 ± 31 1409–1478 (95.4%)
BPN-30009(2) 33315 0.55 -27.9 93.91 ± 0.26 505 ± 22 1410–1450 (95.4%)
Combine BPN- 495 ± 18 1416–1452 (95.4%)
30009
BPN-30006 37459 0.64 -20.73 86.77 ± 0.36 1140 ± 35 830–837 (0.6%)
866–1018 (94.8%)
BPN-30002(1) 28370 1.61 -28.1 86.66 ± 0.30 1150 ± 28 868–993 (95.4%)
BPN-30002(2) 28371 1.45 -31.7 88.10 ± 0.29 1018 ± 26 991–1050 (52.2%)
1078–1145 (43.2%)
Combine BPN- 1080 ± 20 902–915 (3.9%)
30002 970–1026 (91.5%)
BPN-30001(1) 28368 0.75 -30.4 87.65± 0.28 1059 ± 26 903–914 (1.4%)
972–1043 (92.9%)
1090–1100 (1.1%)
BPN-30001(2) 28369 0.62 -28.5 87.55± 0.28 1069 ± 26 900–918 (3.8%)
966–1036 (91.6%)
Combine BPN- 1064 ± 19 984–1028 (95.4%)
30001
Calibration performed with OxCal v 4.2.4 [23] and the SHCal04 calibration curve [24] (by applying a small offset of -21 +/-6 yrs). The two radiocarbon
ages obtained for each crampon BPN-30001 (BPN-30001(1) and BPN-30001(2)), BPN-30002 (BPN-30002(1) and BPN-30002(2)) and BPN-30009 (BPN-
30009(1) and BPN-30009(2)), are related to the same event and were therefore combined before calibration to obtain one calibrated age (notify by
Combine) per crampon.
doi:10.1371/journal.pone.0141052.t001
1180 BP). In the light of this observation and considering the prior information on the coher-
ency between the radiocarbon dates, results can be combined before calibration with a high
degree of certainty (902–915 calAD, 3.9% and 970–1026 calAD, 91.5%). Overall, the calendri-
cal distributions of all three crampons form a coherent chronological group.
Discussion
Crampons BPN-30001 and BPN-30002 were recovered from the 1st terrace and are therefore
directly associated with the initial construction of the Baphuon (see Fig 2). Based on the radio-
carbon results there is a strong correlation of this phase with the end of the 10th century and
the beginning of the 11th century (984–1028 calAD, 95.4% and 970–1026 calAD, 91.5%) and
therefore either with Jayavarman V (968–1000 AD) or with Suryavarman I (1010–1050 AD).
Only one date has been obtained for BPN-30006 (866–1018 calAD, 94.8%) however it too
demonstrates a clear relationship with both kings. These first absolute dates have to be com-
pared with previous interpretations used to argue for the reigns of the three kings who ruled at
Angkor from the late 10th to mid-11th centuries CE. A critical fact underlying this discussion is
that there are no previous archaeological evidence or direct historical accounts attributing the
temporal association of the Baphuon temple. Using inferences based on indirect historical
accounts and mistaken associations to references from two spatially and temporally unrelated
inscriptions (Takeo K.278; Lovek K.136), an initial hypothesis saw construction completed by
Udayadityavarman II (1050–1065 CE) [29]. Consideration of architectural evidence however
suggested that the Baphuon could not be the temple mentioned in the Lovek stele and, as a
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First Direct Dating for the Baphuon Temple
Fig 5. Calibrated (95.4% probability ranges) and modelled radiocarbon dates obtained for iron crampons from the Baphuon temple and from the
reclining Buddha of the western side. The dotted gray box denotes the two sub-samples for each crampon. Results from the Baphuon temple are
compared with the reigns of kings Jayavarman V (968–1000 CE), Suryavarman I (1010–1050 CE) and Udayadityavarman II (1050–1065 CE). Results from
the Reclining Buddha are compared with the period of Ayutthayan occupation at Angkor.
doi:10.1371/journal.pone.0141052.g005
consequence, cannot be associated with the latter king [30]. Inclusion of a third stele (Prah
Ngoc K.289) returned attention to Udayadityavarman II [31] and today remains the standard
association in guidebook and academic publications. Contrary to these interpretations based
on speculation, the new absolute dates suggest that the Baphuon is not associated with Udaya-
dityavarman II. This new conclusion is supported by the comparatively brief (15 years) reign
of this king relative to the considerable scale of the Baphuon construction. From a practical
and logistical perspective, Udayadityavarman II likely would not have the time to plan,
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First Direct Dating for the Baphuon Temple
organize, and complete the construction of the temple. The coherence of the dates obtained
from the different crampons used from the beginning to the completion of the temple makes
us consider the hypothesis of re-use of ancient crampons very improbable. Thus, the results do
place the iron crampons used in the initial construction within the reigns of Jayavarman V and
Suryavarman I. Nevertheless, Jayavarman V is already associated with the Ta Keo temple
mountain that began in the last quarter of the tenth century [32] and therefore precludes the
argument that he similarly funded the Baphuon. On the contrary, Suryavarman I, the king
responsible for consolidating the fractious Khmer elite and re-establishing Khmer dominance
over the region is not yet associated with his own temple mountain, a primary marker of regnal
power of all the great kings of Angkor. Contrary to current views, the cultural contextualization
of the radiocarbon dates strongly suggests that the Baphuon was not founded by Udayaditya-
varman II but rather by his father Suryavarman I.
The modeled radiocarbon date of BPN-30009 from the Reclining Buddha is significantly
earlier than expected (1417–1452 calAD, 95.4%) and cannot be related to a 16th century reuse
of Angkor. Instead it is associated with the Ayutthayan take-over of Angkor between 1431 and
at least 1444 AD. Combined with recent inquiries into the growing evidence for Ayutthayan
presence in Angkor via sculpture [14] and Thai chronicles in the mid-15th century [33,34], the
nature of the decline of Angkor during the 14th-15th centuries must continue to be re-evaluated
with new lines of evidence. The crucial significance of the Reclining Buddha is that it might
precede the Ayutthayan incursion, coincide with it and be their premise monument, or post-
date the incursion and perhaps celebrate its end. This date also coincides with the recent cli-
matic studies that identified repeated episodes of drought and flood during the 14th and 15th
centuries that crippled Angkor’s infrastructure and led to a reordering of political power [5]. A
single date cannot re-write this critical, obscure and important time in Cambodian history yet
the renovation of the Baphuon demonstrates the presence of a Theravada Buddhist state
bureaucracy, either Khmer or foreign, capable of organizing large-scale infrastructure changes
during second period of severe climatic instability.
Conclusion
The first absolute dates recovered from the Baphuon provide important, new insights into the
developmental history of Angkor, the largest pre-industrial city on earth. While far from fixed,
the contextualized results demonstrated previous historical interpretations ignored major
political processes (e.g., the 11th century consolidation and impact of influential king) or over-
interpreted the severity of events (e.g., the 14th–15th century operational capability of the capi-
tal) that help explain the scale of construction and modification of this major monument.
Directly dating iron with low carbon content using the newly developed method represents a
considerable, potential asset for archaeologists, architects and art historians to clarify temporal
sequences of masonry buildings such as Angkor Wat and monuments in other global contexts
(e.g., Egypt, Ancient Greece and Rome, Medieval India) where iron was used as a tie that binds.
Furthermore, this new approach has the potential to revise chronologies related to iron con-
sumption practices since the origins of ferrous metallurgy three millennia ago.
Acknowledgments
This project is indebted to the Baphuon restoration work directed by the late Pascal Royère of
the École Française d’Extrême-Orient (EFEO) and to the Authority for the Protection and Safe-
guarding of Angkor Region Authority (APSARA). Special thanks to Christophe Pottier and
Roland Fletcher for comments on early drafts. We acknowledge the LMC14 team for the radio-
carbon measurements.
PLOS ONE | DOI:10.1371/journal.pone.0141052 November 4, 2015 11 / 13
First Direct Dating for the Baphuon Temple
Author Contributions
Conceived and designed the experiments: SL MH PD. Performed the experiments: SL ED-K
EV. Analyzed the data: SL ED-K MH. Wrote the paper: SL MH.
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