A comprehensive archaeological map of the world’s largest preindustrial settlement complex at Angkor, Cambodia Damian Evans*†, Christophe Pottier‡, Roland Fletcher§, Scott Hensley¶, Ian Tapleyʈ, 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; ʈHorizon 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 scale (5) that provided a much-needed foundation for archaeolog- centuries Common Era (CE)] has for many years been understood ical mapping. as a ‘‘hydraulic city,’’ an urban complex defined, sustained, and However, the burden of the conservation d’Angkor in the 1960s ultimately overwhelmed by a complex water management net- and the dire circumstances of Cambodia from the 1970s to the early work. Since the 1980s that view has been disputed, but the debate 1990s made it impossible to fully realize his agenda: his archaeo- has remained unresolved because of insufficient data on the logical mapping never went beyond the preliminary and raw landscape beyond the great temples: the broader context of the topographic base maps, which remained unpublished until 1993 (6). monumental remains was only partially understood and had not Additionally, these maps were never completed for the area north been adequately mapped. Since the 1990s, French, Australian, and of Angkor Thom, thus reinforcing a longstanding focus on the Cambodian teams have sought to address this empirical deficit central and southern areas at the expense of the northern region. through archaeological mapping projects by using traditional As a result, Groslier continued to use simple schematic maps to methods such as ground survey in conjunction with advanced develop his theory (1) and Angkor remained, until the early 1990s radar remote-sensing applications in partnership with the National and still to some extent even today, only partially understood as a Aeronautics and Space Administration (NASA)/Jet Propulsion Lab- settlement, as an inhabited space in which much of the economic, oratory (JPL). Here we present a major outcome of that research: residential, agricultural, and probably even ritual activity took place a comprehensive archaeological map of greater Angkor, covering beyond the walled enclosures and great stone temples of central nearly 3,000 km2, prepared by the Greater Angkor Project (GAP). Angkor. The map reveals a vast, low-density settlement landscape inte- Since the early 1990s, successive cartographic projects have grated by an elaborate water management network covering sought to address this empirical deficit by producing detailed >1,000 km2, the most extensive urban complex of the preindustrial archaeological maps of the Angkor region. These maps include the world. It is now clear that anthropogenic changes to the landscape main temples but also detail the residential areas, fields, and were both extensive and substantial enough to have created grave infrastructure that stretched far beyond the massive sandstone challenges to the long-term viability of the settlement. constructions (7–10). In the 1990s, the temple-centric focus of Angkorian studies was, for the first time, comprehensively chal- archaeology ͉ geographic information systems ͉ remote sensing ͉ lenged by the development of a new map of the central and southern Southeast Asia ͉ urbanism areas of Angkor by Christophe Pottier of the EFEO (9, 10). His work originally grew out of the need to map and document the he first century of scholarship on Angkor, in Cambodia, was landscape of Angkor for the purposes of the United Nations Tdominated by the need to conserve and restore the monuments, Educational, Scientific, and Cultural Organization (UNESCO) to locate Khmer civilization within broader cultural history, and to World Heritage nomination and site management. Noticing the establish a basic chronological framework for Angkor and its puzzling dichotomy between the clusters of monuments on the Southeast Asian empire [9th–16th centuries Common Era (CE)]. In earlier maps and the hundreds of newly identified local temples the early 1950s, Bernard-Philippe Groslier of the E´cole Franc¸aise dispersed across the landscape, Pottier then developed the mapping d’Extreˆme-Orient(EFEO) became the first scholar to pay serious on a more precise scale by collating existing maps and documen- attention to the traces of a hydraulic network that had been partially tation, analyzing aerial photographs and undertaking systematic mapped in the first half of the 20th century. Groslier surmised that field surveys. His final map, completed in 1999 (10), thus docu- it was both built and used for irrigation, specifically, to ameliorate mented a built landscape of occupation mounds, local temples, and variations in agricultural output caused by an unpredictable annual household ponds interspersed among the great monuments and the monsoon and to support a huge population of greater than a million hydraulic works associated with them (Fig. 1). people (1) in a constellation of suburbs. He also argued that the extent and breakdown of the network was implicated in the demise Author contributions: D.E., C.P., R.F., and M.B. designed research; D.E., C.P., S.H., I.T., and ANTHROPOLOGY of Angkor (1, 2). 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. As one of the very few scholars in the 20th century with both an wrote the paper. awareness of and an interest in the settlement pattern surrounding The authors declare no conflict of interest. the monuments, Groslier also understood that a comprehensive This article is a PNAS Direct Submission. and integrated program of archaeological research, including Abbreviation: CE, Common Era. ground survey, remote sensing, and archaeological mapping, was †To whom correspondence should be addressed at: Archaeological Computing Laboratory, needed to broaden the perspective beyond the great monuments Madsen Building F09, University of Sydney, NSW 2006, Australia. E-mail [email protected]. and to provide a firm basis for assessing his theory (1–5). Impor- usyd.edu.au. tantly, he commissioned topographic maps of Angkor at 1:10,000 © 2007 by The National Academy of Sciences of the USA www.pnas.org͞cgi͞doi͞10.1073͞pnas.0702525104 PNAS ͉ September 4, 2007 ͉ vol. 104 ͉ no. 36 ͉ 14277–14282 Downloaded by guest on September 25, 2021 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 hand- drawn 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 data acquired over An- gkor in September 2000 by NASA/JPL on behalf of GAP (18), expanding on previous radar data acquisitions in 1994 on behalf of the World Monuments Fund (SIR-C/X-SAR) and in 1996 on behalf of Elizabeth Moore of the University of London, London, U.K. (AIRSAR). The first stage of GAP’s analysis, begun in 2001 and completed in 2002, was undertaken with a view to very quickly producing a ‘‘broad-brush’’ picture of the settlement pattern to the north of Pottier’s study area. The specific aims were to gain an understanding of the interaction of microwave sensors with the archaeological landscape, to develop and refine methods of sys- tematically applying imaging radar to an archaeological investiga- tion, and to assess the feasibility and likely outcome of a more Fig. 1. Oblique aerial views of remnant Angkorian urban features. (Upper detailed survey incorporating heterogeneous data sources. Left) Occupation mounds and ponds. (Upper Right) Canals and embankments. The AIRSAR instrument is an active sensor with the ability to (Lower Left) Multifunction roadway/canals. (Lower Right) Classic ‘‘village penetrate clouds. On its 2000 deployment over Angkor, multiple temple’’ configuration. channels of data (C band at 3 cm, L band at 25 cm, and P band at 64 cm, with polarisation measured at transmit and receive) were aquired over Ϸ8,000 km2 through 98% cloud cover. The ability of Pottier also showed decisively that the great reservoirs, or barays, the AIRSAR instrument to produce high-quality, high-resolution had inlets and outlets and were connected to a network of channels data sets describing surface roughness and electrical properties is and embankments, contrary to the assertions of critics of Groslier’s well documented [Jet Propulsion Laboratory (2006) AIRSAR Air- hydraulic thesis from the 1980s onwards (11–14). Moreover, the borne Synthetic Aperture Radar Documentation. Available at http:// longstanding assumption (2, 11) that the extensive