A comprehensive archaeological map of the world’s
largest preindustrial settlement complex
at Angkor, Cambodia
Damian Evans*†
, Christophe Pottier
‡
, Roland Fletcher
§
, Scott Hensley
¶
, Ian Tapley
, Anthony Milne**,
and Michael Barbetti
††
*Archaeological Computing Laboratory and
§
Department of Archaeology, University of Sydney, Sydney NSW 2006, Australia;‡
E´cole Franc¸aise
d’Extreˆme-Orient, Siem Reap, Cambodia;
¶
National Aeronautics and Space Administration Jet Propulsion Laboratory, 4800 Oak Grove Drive,
Pasadena, CA 91109;
Horizon Geoscience Consulting, Perth WA 6020, Australia; **School of Biological, Earth and Environmental Sciences,
University of New South Wales, Sydney NSW 2052, Australia; and††
School of Physical Sciences, University of Queensland,
Brisbane QLD 4072, Australia
Edited by Michael D. Coe, Yale University, New Haven, CT, and approved June 29, 2007 (received for review March 17, 2007)
The great medieval settlement of Angkor in Cambodia [9th–16th
centuries Common Era (CE)] has for many years been understood
as a ‘‘hydraulic city,’’ an urban complex defined, sustained, and
ultimately overwhelmed by a complex water management network. Since the 1980s that view has been disputed, but the debate
has remained unresolved because of insufficient data on the
landscape beyond the great temples: the broader context of the
monumental remains was only partially understood and had not
been adequately mapped. Since the 1990s, French, Australian, and
Cambodian teams have sought to address this empirical deficit
through archaeological mapping projects by using traditional
methods such as ground survey in conjunction with advanced
radar remote-sensing applications in partnership with the National
Aeronautics and Space Administration (NASA)/Jet Propulsion Laboratory (JPL). Here we present a major outcome of that research:
a comprehensive archaeological map of greater Angkor, covering
nearly 3,000 km
2
, prepared by the Greater Angkor Project (GAP).
The map reveals a vast, low-density settlement landscape integrated by an elaborate water management network covering
>1,000 km
2
, the most extensive urban complex of the preindustrial
world. It is now clear that anthropogenic changes to the landscape
were both extensive and substantial enough to have created grave
challenges to the long-term viability of the settlement.
archaeology geographic information systems remote sensing
Southeast Asia urbanism
T
he first century of scholarship on Angkor, in Cambodia, was
dominated by the need to conserve and restore the monuments,
to locate Khmer civilization within broader cultural history, and to
establish a basic chronological framework for Angkor and its
Southeast Asian empire [9th–16th centuries Common Era (CE)]. In
the early 1950s, Bernard-Philippe Groslier of the E ´cole Franc ¸aise
d’Extreˆme-Orient (EFEO) became the first scholar to pay serious
attention to the traces of a hydraulic network that had been partially
mapped in the first half of the 20th century. Groslier surmised that
it was both built and used for irrigation, specifically, to ameliorate
variations in agricultural output caused by an unpredictable annual
monsoon and to support a huge population of greater than a million
people (1) in a constellation of suburbs. He also argued that the
extent and breakdown of the network was implicated in the demise
of Angkor (1, 2).
As one of the very few scholars in the 20th century with both an
awareness of and an interest in the settlement pattern surrounding
the monuments, Groslier also understood that a comprehensive
and integrated program of archaeological research, including
ground survey, remote sensing, and archaeological mapping, was
needed to broaden the perspective beyond the great monuments
and to provide a firm basis for assessing his theory (1–5). Importantly, he commissioned topographic maps of Angkor at 1:10,000
scale (5) that provided a much-needed foundation for archaeological mapping.
However, the burden of theconservation d’Angkorin the 1960s
and the dire circumstances of Cambodia from the 1970s to the early
1990s made it impossible to fully realize his agenda: his archaeological mapping never went beyond the preliminary and raw
topographic base maps, which remained unpublished until 1993 (6).
Additionally, these maps were never completed for the area north
of Angkor Thom, thus reinforcing a longstanding focus on the
central and southern areas at the expense of the northern region.
As a result, Groslier continued to use simple schematic maps to
develop his theory (1) and Angkor remained, until the early 1990s
and still to some extent even today, only partially understood as a
settlement, as an inhabited space in which much of the economic,
residential, agricultural, and probably even ritual activity took place
beyond the walled enclosures and great stone temples of central
Angkor.
Since the early 1990s, successive cartographic projects have
sought to address this empirical deficit by producing detailed
archaeological maps of the Angkor region. These maps include the
main temples but also detail the residential areas, fields, and
infrastructure that stretched far beyond the massive sandstone
constructions (7–10). In the 1990s, the temple-centric focus of
Angkorian studies was, for the first time, comprehensively challenged by the development of a new map of the central and southern
areas of Angkor by Christophe Pottier of the EFEO (9, 10). His
work originally grew out of the need to map and document the
landscape of Angkor for the purposes of the United Nations
Educational, Scientific, and Cultural Organization (UNESCO)
World Heritage nomination and site management. Noticing the
puzzling dichotomy between the clusters of monuments on the
earlier maps and the hundreds of newly identified local temples
dispersed across the landscape, Pottier then developed the mapping
on a more precise scale by collating existing maps and documentation, analyzing aerial photographs and undertaking systematic
field surveys. His final map, completed in 1999 (10), thus documented a built landscape of occupation mounds, local temples, and
household ponds interspersed among the great monuments and the
hydraulic works associated with them (Fig. 1).
Author contributions: D.E., C.P., R.F., and M.B. designed research; D.E., C.P., S.H., I.T., and
A.M. performed research; D.E., C.P., R.F., S.H., I.T., and A.M. analyzed data; and D.E. and R.F.
wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Abbreviation: CE, Common Era.
†
To whom correspondence should be addressed at: Archaeological Computing Laboratory,
Madsen Building F09, University of Sydney, NSW 2006, Australia. E-mail evans@acl.arts.
usyd.edu.au.
© 2007 by The National Academy of Sciences of the USA
www.pnas.orgcgidoi10.1073pnas.0702525104 PNAS September 4, 2007 vol. 104 no. 36 14277–14282
ANTHROPOLOGY
Pottier also showed decisively that the great reservoirs, orbarays,
had inlets and outlets and were connected to a network of channels
and embankments, contrary to the assertions of critics of Groslier’s
hydraulic thesis from the 1980s onwards (11–14). Moreover, the
longstanding assumption (2, 11) that the extensive agricultural field
systems visible on the surface today might date from Angkorian
times was supported by his new map, which displayed the integral
connection between the local temples and their agricultural space
(15). Various other elements of the classical Angkorian landscape,
in particular, the small ponds described in an account of Angkor in
the 13th century (16), have also persisted on the surface, were
clearly identifiable from the air and have often been renovated and
reused by the contemporary Khmer population. Archaeological
evidence of Angkorian occupation (in particular, brick and ceramic
debris) was consistently found at the sites that had been identified
from the air and was documented and collected wherever appropriate (10). Field verification continues across the greater Angkor
region in a process that has consistently matched aerial observations
with surface evidence. Recent excavations at the Siem Reap airport
(17) and elsewhere have provided further stratigraphic evidence of
continuity between subtle topographic features visible on the
surface today and the urban landscape of medieval Angkor.
Pottier’s new study used the maps commissioned by Groslier as
a cartographic base (because they were the only available ones at
that time), and began the process of creating a comprehensive
archaeological map of Angkor by recording several thousand of
these features and part of agricultural field system within an area of
1,000 km
2
. The coverage of that survey was limited to the
southern and central parts of Angkor by the available cartographic
base and by the persistent security risks in Siem Reap Province until
1998. However, it was clear from remote sensing that the contiguous
settlement space of Angkor extended well beyond what had been
mapped; further survey was therefore required.
Since the completion of Pottier’s initial mapping in 1999, the
Greater Angkor Project (GAP), an international research program
(Australian, Cambodian, and French) focusing on the spatial
structure, the water management network, and the reasons for the
decline of Angkor, has continued to extend the spatial coverage of
detailed archaeological mapping by using a diverse range of data
sources, field techniques, and, notably, airborne imaging radar
(AIRSAR) data acquired for GAP in 2000 by National Aeronautics
and Space Administration (NASA)/Jet Propulsion Laboratory
(JPL).
Mapping
One of the first tasks was the digitization of Pottier’s 1999 handdrawn map and the conversion of its data into a geographic
information system. Subsequent mapping work has concentrated
on the use of airborne radar imaging (AIRSAR/TOPSAR) for
archaeological survey, in particular using da
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