Southeast Asian Studies, Vol. 46, No. 4, March 2009

Application of Geo-Informatics to the Studyof the Royal Road from Angkor to Phimai

Surat LERTLUM* and SHIBAYAMA Mamoru**

Abstract
Geo-informatics technologies are utilized in the conservation and management of cultural heritageand in related studies. For example, remote sensing (RS) and Geographical Information System(GIS) technologies are utilized as tools for archaeological analysis together with conventional
methods. Around the world, RS and GIS technologies have been used to assist archaeologists to
pinpoint and identify archaeological sites. With reference to these applications of geoinformatics, the Living Angkor Road Project came up in 2005 with the concept of integrated
studies based on interdisciplinary collaboration in an archaeological study in Thailand andCambodia [Lertlum et al. 2007]. In this project, archaeological and anthropological knowledge
was used together with geo-informatics, information and geo-physics technologies to identify,
pinpoint and study the ancient road from Angkor in Cambodia to Phimai in Thailand that is
described in the inscription of the Pra Khan temple in Angkor, Cambodia.
Application of geo-informatics to this project revealed the following results: (1) Application of
GIS/RS conﬁrmed the hypothesis proposed by archaeologists based on the Pra Khan inscriptionthat an ancient road once ran from Angkor in Siem Reap area of Cambodia to Phimai in Nakorn
Ratchasima, Thailand. In particular, parts of the ancient road were clearly recognized byanalyzing the archaeological sites found standing along a line on satellite images and aerial
photographs. (2) Buildings and facilities related with the ancient road, such as ancient bridges,
ancient industry sites, and dharmshalas (rest-house chapels), were newly discovered through thesame analysis. (3) Predictions and assumptions derived from RS/GIS methodologies wereveriﬁed by ﬁeld surveys conducted by specialists in archaeology, anthropology, and informatics.
In other words, RS/GIS methodologies also could be used to decide an area of ﬁeld survey inadvance. This approach in area studies exactly corresponds to one of the proposed
methodologies of Area Informatics [Shibayama 2005].
This paper describes the role and signiﬁcance of geo-informatics in the study of the royal roadfrom Angkor to Phimai, presents new ﬁndings obtained from application of geo-informatics inarchaeological studies, describes how GIS/RS technologies were applied, and discusses
effectiveness of applying the satellite image ASTER1) and SRTM2) elevation data in the project.
Keywords : Angkor, archaeology, area study, geo-informatics, Phimai, remote sensing and GIS,
royal road

* Chulachomklao Royal Military Academy, Thailande-mail: surat@ait.ac.th** 柴山 守，Center for Southeast Asian Studies, Kyoto University
e-mail: sibayama@cseas.kyoto-u.ac.jp
1) ASTER (Advanced Spaceborne Thermal Emission and Reﬂection Radiometer): It can be used forgeological survey, resource exploring, and monitoring global warming, acid rain, and so on. Resolution is
15 m. Scanning width is 60 km. Scanning interval is 16 days.
2) SRTM (Shuttle Radar Topographic Mission): The SRTM is digital elevation data produced by NASAoriginally. URL: http://srtm.csi.cgiar.org/Index.asp
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東南アジア研究I

46巻 4 号

Introduction

Geo-informatics technologies have recently been utilized effectively in many applications to areastudies in various ﬁelds of analyses, such as land use/land cover change, urban studies,movement of human activities, archaeological and historical studies on conservation,
preservation, management of cultural heritage, and in other related studies.

For example, inarchaeological and historical studies, GIS/RS can be used as tools for archaeological analysis.
In various cases around the world, geo-informatics technologies in the form of RS and GIS havebeen used to assist archaeologists to pinpoint and identify archaeological sites.

Examplesinclude the discovery of a buried section of the Great Wall of China by analyzing SIR-C3) radar
data from the space shuttle [Associated Press 2009].

It had never been imagined before how

geo-informatics technologies could effectively assist the conventional methods of archaeologists.
The application of SIR-A4) to the lost city of Ubar [Blom et al. 1997] and AirSAR at Angkor are
two of the best-known studies [Lertlum et al. 2001a].
From 2005 to 2008, the Living Angkor Road Project (project leaders: Surat Lertlum(Thailand) and Im Sokrithy (Cambodia)) was conducted by researchers from Chulachomklao
Royal Military Academy, Silpakorn University, Prince of Songkla University, Fine Arts
Department of Thailand and researchers from APSARA Authority,5) Cambodia with funding
support from the Thailand Research Fund (TRF).

This project involved detailed studies of theroyal road from Angkor to Phimai, its utilization, the people who lived and used the royal road,and the culture that has now disappeared.

The most advanced technologies in the project

were technologies of RS, GIS, geo-physics, and information technology and these were employed
together with conventional archaeological methods.

Also, in order to share information anddata effectively among collaborating scholars, an information sharing system which includes
gathering and retrieval functions was newly developed.

In addition, it was considered that thedata derived from the project could be further utilized in related works in the ﬁelds of land use
planning and urban development related to cultural management, tourism, and so on.
Even though the application of geo-informatics to cultural studies is still a new ﬁeld ofstudy, it is proving to be an indispensable adjunct to conventional methods of cultural studies.
However, the ways in which geo-informatics is applied to cultural studies might vary from caseto case and location to location.
This paper illustrates how geo-informatics was applied to study the royal road from
Angkor to Phimai and the results which were newly obtained.

Also, the role and signiﬁcance3) SIR-C (Spaceborne Imaging Radar-C): The SIR-C is part of an imaging radar system that was ﬂown onboard two Space Shuttle ﬂights (9-20 April, 1994 and 30 September-11 October, 1994). The USGS
distributes the C-band (5.8 cm) and L-band (23.5 cm) data. URL: http://eros.usgs.gov/products/satellite/
sirc.php
4) SIR-A: See above footnote 3). The SIR-A used an L-band SAR HH-polarized system, which was capableof 40 m resolution in images whose swath widths were 50 km (31 mi).
5) APSARA Authority: Authority for the Protection and Management of Angkor and the Region of Siem
Reap, URL http://www.autoriteapsara.org/en/apsara.html
548

S. LERTLUM and SHIBAYAMA M. : Application of Geo-Informatics to the Study of the Royal Road from Angkor to Phimaiof applying geo-informatics to the archaeological studies are introduced.

II

Geo-spatial Data Processing in Cultural Studies

From the view point of data availability, the geo-spatial data that can be utilized for cultural
studies is quite different from that employed in other applications, such as census analysis,
measured data analysis, and so on.

In other words, it is difﬁcult to separate the gathering andprocessing of data in terms of phases of input, processing, and output, which is the general
pattern of information processing.

The informatics specialist must understand the meaning ofdata and the story of the past in order to analyze it appropriately.

Therefore, data that can tell

us about the past can be utilized only in collaborative work between informatics specialists andarchaeologists.

In most of cases, archaeological studies treat events that occurred before any

geo-spatial data was recorded or produced.

The best solution in this kind of study is to utilize

the oldest data available, such as old aerial photographs, old maps and ancient documents[Lertlum 2003a].

This is probably the most valuable information that we can acquire when weneed to study further back in time.

In addition, in the current situation, high resolution satellite

images such as QuickBird and IKONOS are also available, but at a high cost.

The utilization ofexisting aerial photographs is still an alternative way to analyze a target area with comparable
results to high resolution satellite images [Lertlum and Moore 2005].
In utilizing old aerial photographs for area studies, the most effective way is to integrate theold aerial photographs with other materials, such as current aerial photographs, satellite images,
and the GIS database with geo-referencing information [ibid.].
utilizing old aerial photographs.

This is the critical point ofSince old aerial photographs generally lack geo-referencing

information, such as latitude and longitude at the corners of the photograph, it is difﬁcult to mapthem onto other materials accurately.

Therefore, the main issue with old aerial photographs

lies in geo-referencing them accurately with other material in terms of position and scale.

Tosolve this issue, the geo-referencing information from current aerial photographs, satellite
images, and/or the GIS database can be used for integrating the old aerial photographs.

For

example, Fig. 1 illustrates a sample of geo-referencing of old aerial photographs with an imageof Landsat ETM6) for the Angkor area.

The technologies mentioned above also were applied in

the project.

III

Use of Geo-informatics for Area Studies in a Multi-disciplinary
Approach: The Study of the Royal Road from Angkor to Phimai

In this research, archaeological and anthropological knowledge together with geo-informatics,
6) Landsat ETM: Landsat with the Enhanced Thematic Mapper sensor. The ETM instrument included aneighth band with a spatial resolution of 30 m. This data can be applied for land use mapping, geology,hydrology, environmental monitoring, and so on.
URL: http://landsat.gsfc.nasa.gov/about/549

東南アジア研究46巻 4 号

東南ア4604-5,1

Fig. 1 A Sample of Geo-referencing of Old Aerial Photographs with Image of Landsat ETM (2002) for
the Angkor Area

geo-physics and information technologies was utilized to identify and pinpoint the ancient roadfrom Angkor to Phimai that was described in the inscription about Jayavarman VII, the great
king of Cambodia.

From archaeological and historical studies, we had learnt that during his

reign, the Khmer empire expanded to cover most of Southeast Asia.

The Pra Khan inscription

mentions that Jayavarman VII built infrastructures for travelers, such as 17 dharmshalas (resthouse chapels) along the royal road from Angkor to Phimai [Cœdès 1941].
This research aims to study the details of this ancient road, its utilization, the people who
lived along and used the road, the ancient industries along it, and the cultures that havedisappeared or that have continued to ﬂourish.

The most advanced technologies were appliedin the ﬁeld of RS, GIS, archaeology, anthropology, geo-physics and information technology.
Information systems were also developed to gather data from this study for scholars to use.

In

addition, the data derived from this project can be further utilized for related works in the ﬁeldsof land use planning related to cultural management, tourism, and so on.
The steps taken in this study were as follows:(a) Review of previous studies about the royal road from Angkor to Phimai to identify ingeneral the science and technologies that can be utilized, and what results can be expectedfrom the proposed study.
(b) Preliminary analysis to utilize the result to develop a GIS database for ﬁeld survey
planning.
(c) Conducting ﬁeld surveys.
550

S. LERTLUM and SHIBAYAMA M. : Application of Geo-Informatics to the Study of the Royal Road from Angkor to Phimai(d) Conducting geo-physics experiments.
(e) Conducting archaeological excavations.
(f) Developing GIS database from ﬁeld surveys together with other related data for
integrated analysis.
(g) Integrated analysis with all information.
(h) Proof of assumptions from the results of the integrated analysis.
The following explains how we utilized geo-informatics for this study.

Section III. 1

explains how we applied geo-informatics at the beginning of the study in making survey plans(step (b)).

Section III. 2 explains how we applied geo-informatics to the data from surveys(steps (f) and (g)).
III. 1 Utilization of Remote Sensing and GIS for Survey Planning
In order to start the research work according to the proposed plan [Lertlum et al. 2007], existingarchaeological data related to the royal road as gathered.

Then, the GIS database was

implemented to make a preliminary study of the royal road from all related geo-informatics
data, including old maps, aerial photos, satellite images, and location databases of allarchaeological sites in the study area.

A buffer zone7) was created around the linked pathconnecting the already known dharmshalas.
ﬁeld survey.

Next, the database was used to make plans for a

From analysis of this database, some parts of the royal road could be identiﬁed

based on assumptions and knowledge about the pattern of the royal road, especially, in

東南ア4604-5,2Fig. 2 Ancient Road Running West from Angkor over Landsat ETM (2000)
7) Buffer zone: One of functions which provided by GIS technologies. This function allows users to specify
appropriate buffer area from the original point, line, and polygon.
551

東南アジア研究46巻 4 号

Cambodia, where the landscape has not changed greatly, but conﬁrmation from the surveys wasneeded.

The following items are the phases that were carried out:

(1) The topographic properties such as surrounding landscape, waterways, and the linear
pattern of the ancient road that can be identiﬁed from satellite images or aerial photographs, as
shown in Fig. 2, were listed as common properties of the ancient road.

This process was done

manually since the classiﬁcation process could not separate between the patterns of the ancientroad and current roads.

In this case, we utilized the ancient road from Angkor to the west as

our sampling site (the ancient road running west from Angkor to Sadok Kok Thom temple near
the Thai border).

The ancient road can be recognized, as shown by the arrows.

(2) The locations of all the previously identiﬁed dharmshalas along the royal road from Angkor
to Phimai were utilized together with aerial photos and satellite images.

In particular, old

東南ア4604-5,3Fig. 3 Dharmshalas (yellow dots) along the Royal Road on Landsat ETM (2000)
Note: Pr stands for Prasat (stone temple).
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S. LERTLUM and SHIBAYAMA M. : Application of Geo-Informatics to the Study of the Royal Road from Angkor to Phimai

aerial photographs, (World Wide series from U.S. Army taken in 1954 and the Williams-Huntcollection taken during World War II) which show little disturbance of the landscape were georeferenced and overlaid.

Such satellite images and aerial photographs were used together

with the information from step (a) to trace the royal road and plan ﬁeld surveys.

In addition,

the patterns of the landscape around the known dharmshalas along the royal road, a sample ofwhich is shown in Fig. 3, were compared.

We found that all the dharmshalas are located near awater structure or waterway.
(3) Man-made structures along the royal road were identiﬁed. For example, water structures,ancient laterite bridges (see Fig. 14), and ancient communities in a 1-km buffer zone on bothsides of the road were explored from satellite images, aerial photographs, archaeological data,and previous survey data.

This was easily performed using a function in the GIS.

also was used for planning ﬁeld surveys.

This result

Fig. 4 shows the landscape of the ancient communityof Muang Fai from an old aerial photograph (World Wide series: 1954).

Muang Fai is an

important ancient city of northeast Thailand.

From the buffering process, Muang Fai lies

within the 1-km buffer zone of the royal road.

This information is also very important for

illustrating the relationship of the royal road to the ancient communities in the area.
(4) To identify two missing dharmshalas, the information about the characteristics of locations
selected for dharmshalas from (2) together with the topography of the surrounding werecompared with the possible locations of the two missing dharmshalas.

The next step was toinvestigate whether the possible locations located near ancient communities, ancientwaterways, and whether the distance was within the average distance between dharmshalas(calculated to be approximately 15 km from the known locations of dharmshalas in Cambodia).
As a result, the possible locations of the two missing dharmshalas were located and identiﬁed byﬁeld surveys, as shown in Figs. 5 and 6.

One rest house is Prasat Kok Phnov in Figs. 5 and東南ア4604-5,4Fig. 4 Ancient Community Muang Fai in 1954 Aerial Photograph553

東南アジア研究46巻 4 号

東南ア4604-5,5Fig. 5 Location of Prasat Kok Phnov and the Predicted Area (Circled)(Topographic map 1 : 50,000)

東南ア4604-5,6Fig. 6 Location of Prasat Ampil and the Predicted Area (Circled)(Topographic map 1: 50,000)
554

S. LERTLUM and SHIBAYAMA M. : Application of Geo-Informatics to the Study of the Royal Road from Angkor to Phimai

13(b); the other is Prasat Ampil in Figs. 6 and 13 (a).

These processes required manualinterpretations from the experts of the factors listed above, since the criteria were too complex
for any available GIS software.
(5) To identify the royal road passing Dong Rek mountain, the integrated activities of GIS
analysis and interviews in the local community were conducted.

The location of the royal road

東南ア4604-5,7aFig. 7a

Elevation in the Area of the Royal Road Passing
over Dong Rek Mountain[SRTM data (90 m. resolution)]
Note: dark gray-＞light gray: low-＞high elevation

東南ア4604-5,7bFig. 7b

Detail of Royal Road Passing over Dong Rek Mountain[SRTM data (90 m. resolution)]555

東南アジア研究46巻 4 号

pass through Dong Rek mountain was ﬁrst approximated by analysis of the elevation data
(SRTM), as shown in Fig. 7, to identify the lowest slope area in the vicinity of the royal roadcrossing the Ta Mean pass.

This prediction was based on location data of the Ta Mean

dharmshala on Dong Rek mountain and related information.

東南ア4604-5,8-1

The location of the pass was

東南ア4604-5,8-2(1) Scenery of the Road

(2) Shoulder of the Road

東南ア4604-5,8-3(3) Road in Satellite Image (IKONOS, 2003)
Fig. 8 Road over the Dong Rek Mountain556

S. LERTLUM and SHIBAYAMA M. : Application of Geo-Informatics to the Study of the Royal Road from Angkor to Phimai

conﬁrmed by the ﬁeld survey.

To ﬁnd the approximate location of the pass, we used the resultof SRTM analysis of the slope and aspects of the area surrounding Ta Mean dharmshala
onward to the Cambodia side of the royal road.

From the slope and aspects of the area, wefound that the lowest slope area is located on the southeast of Ta Mean dharmshala and Ta
Mean Thom (an important Khmer temple southeast of Ta Mean).

Since the area was thought

to still contain many land mines, the next step was to interview members of the local
community about the history of the pass and in what direction that their ancestors had used thepass over the mountain.
analysis.

The result of the interviews corresponded with the result from our

Their ancestors had used the path on the southeast of Ta Mean dharmshala to crossthe Dong Rek mountain.
dharmshala.

We then surveyed the path on the southeast of Ta Mean

As a result, we discovered that the ancient road over the pass was constructed oflaterite, as shown in Fig. 8.
III. 2 Analysis of Survey Data
After the surveys, the information and data collected from all ﬁelds of study, including locationsof archaeological sites, archaeological samples, topographical situation, and location of ancient
communities, were integrated and analyzed.

In this study, experience had shown that RS and

GIS technologies alone cannot be utilized effectively in archaeological research.

In order toachieve the aim of a project to identify and study the details of the royal road from Angkor to
Phimai, a multi-disciplinary approach is the most signiﬁcant and suitable.

The results of theanalysis are as follows:

東南ア4604-5,9Fig. 9 Sample of the Network of Ancient Roads to Ancient
Communities in Cambodia
Source: APSARA authority, Cambodia
557

東南アジア研究46巻 4 号

(1) Identifying the Ancient Road Network
From the ﬁeld surveys and RS/GIS and archaeological analyses, we learned that the ancientroad was not a single road, but it consisted of a network of ancient roads to ancient communities
and ancient industries.
ancient roads.

By utilizing GIS analyses, we identiﬁed the function of these small

The result of this part of the study illustrates the effectiveness of GIS analyses.

Fig. 9 illustrates a sample of the network of ancient roads in Cambodia, where there are two
small ancient roads connecting the royal road to nearby ancient communities.
(2) Identifying the Relationship between Ancient Industry and the Royal Road
The relationship between ancient industry and the royal road was identiﬁed by mapping theancient industry sites from the surveys in the buffer zone of the royal road.

From the mapping,ancient industry sites, such as ceramic kiln sites and iron smelting sites, were found to beconcentrated in the vicinity of the royal road.

The highest concentration of ancient industry

sites along the royal road from Angkor to Phimai are located in Ban Krud, Burirum Province,
Thailand near the border with Cambodia.

Part of this area is illustrated in Fig. 10.

東南ア4604-5,10

Fig. 10The Relationship between Ancient Industry and the RoyalRoad in Ban Krud, Burirum Province, Thailand with
Landsat ETM (2000) as Background
Note: The red dots are ceramic kiln sites. The yellow dots are ironsmelting sites.
558

In

S. LERTLUM and SHIBAYAMA M. : Application of Geo-Informatics to the Study of the Royal Road from Angkor to Phimai

addition, the artifacts collected during the surveys could be identiﬁed as products from theseancient industry sites. The mapping of these ancient industry sites was valuable evidence theroyal road was used for transporting goods between Angkor and Phimai.
(3) Remote Sensing for Geology Analysis of Ancient Industry Sites
In the case of the iron smelting industry, we utilized the ASTER satellite images to analyze theraw material that was used for the iron smelting process.

Archaeological analysis of the ironsmelting sites in Ban Krud, Burirum Province, Thailand, in the buffer zone of the royal road, as
mentioned in (2), indicated that the raw material for the iron smelting industry must be lateritewith sufﬁciently high iron content.

We utilized the ASTER images of the area to calculate its

geological index.8) In this case, we calculated the geological index from the ratio of band 4 and5 from ASTER.

A high index value indicates the concentration of laterite.

From thecalculation, it was considered that the area was once rich in laterite, as shown in Fig. 11.
light color in Fig. 11 means a high density of laterite.

The

However, we could not use this analysis

alone to prove assumption about the geology of the area, since the geological index from ASTER
can be affected by the land cover.

We then also performed a geo-physics analysis of thestudied area, including the study of magnetic anomaly and rock types, which also indicated thatthe area was rich in laterite.

From these studies, it was concluded that one reason that thearea was selected for setting up ancient industry sites was because of the presence of the raw
material to produce iron.
In terms of the environment, the satellite images and aerial photographs show that the area
was formerly dense forest, providing an important source of ﬁrewood.

In addition, analysis of

SRTM showed that all the ancient industry sites that we identiﬁed were located on the highground of an ancient ﬂood plain, as shown in Fig. 12.

IV

Discussion: Geo-informatics in Cultural Studies

This paper has described one application of geo-informatics technologies to cultural studies
through a case study of the royal road from Angkor to Phimai.

In a multi-disciplinary study,

the important point in the research process is for researchers to understand the approaches
that were selected.
research differs.

In each participating discipline, the environment and methodology for

Therefore, researchers have to take into consideration how to apply geo-

informatics technologies to cultural studies.

The environment of the landscape together withthe objective and the data available are the most important elements to be considered before astudy can be conducted.

On the other hand, in most cases, geo-informatics technology alone

cannot be applied to research, especially in cultural studies.

Related ﬁelds of research need tobe utilized in order to accomplish the mission of the project in the form of a multidisciplinary
8) Characteristics of geological components.
geological characteristics.

The satellite image ASTER can be used for sensing the559

東南アジア研究46巻 4 号

東南ア4604-5,11Fig. 11

ASTER Geological Index of Ban Krud Area with Ancient Industry Sites[Geological Index (Channel 4/5) image]
Note: dark green-＞medium green-＞light green: low-＞medium-＞high laterite content
The red dots are iron smelting sites. The blue and purple dots are ceramic kiln sites.

東南ア4604-5,12Fig. 12 SRTM Image of Ban Krud Area with Ancient Industry Sites
Note: dark green-＞medium green-＞light green: low-＞medium-＞high elevation
The red dots are iron smelting sites. The blue and purple dots are ceramic kiln sites.

approach.
In the present study, we discovered several features of the ancient road.

The most

important items are as follows: (1) Two missing dharmshalas were identiﬁed, as shown in
Fig. 13.

(2) Ancient laterite bridges were found along the ancient road in Cambodia, as shownin Fig. 14.

(3) Ancient industry sites were conﬁrmed along the ancient road in both Cambodia

and Thailand, as shown in Fig. 15. (4) Ancient communities were identiﬁed along the ancientroad in both Cambodia and Thailand.
560

S. LERTLUM and SHIBAYAMA M. : Application of Geo-Informatics to the Study of the Royal Road from Angkor to Phimai

東南ア4604-5,13a

東南ア4604-5,13b(a) Prasat Ampil(b) Prasat Kok Phnov

Fig. 13

Identiﬁed Missing Dharmshalas

東南ア4604-5,14a

東南ア4604-5,14b

Fig. 14東南ア4604-5,15a

Identiﬁed Ancient Bridges

東南ア4604-5,15b

Fig. 15 Field Survey in One of Ancient Industry Sites
Source: APSARA authority, Cambodia
561

東南アジア研究46巻 4 号

We have also developed information servers9) to contain all the information from thisresearch project, so that other scholars can access this information.

In addition, we havedeveloped 3D models of dharmshalas, arogyashalas (hospital chapels), and ancient bridges thatwill be utilized in the simulation of ancient life along this ancient road.

This simulation will be

used as a learning tool for the younger generation in the near future.
In the second phase of this study, which was started in 2007, we studied the details ofancient communities and ancient industry sites along the royal road, the results of which can beutilized for eco-tourism purposes in the area along the royal road, especially in the area at theborder of Thailand and Cambodia.

V

Conclusion

The application of GIS/RS in this project has conﬁrmed the hypothesis proposed byarchaeologists based on the Pra Khan inscription that an ancient road once ran from Angkor in
Cambodia to Phimai in Northeast Thailand.

In particular, part of the ancient road was clearlyrecognized by analyzing the archaeological sites standing along a line on aerial photographs andsatellite images.

In this research, archaeological and anthropological knowledge together with

geo-informatics, geo-physics and information technologies were utilized to identify and pinpoint
the ancient road from Angkor to Phimai.

The target area of a ﬁeld survey could be estimatedin advance more accurately using GIS/RS technologies compared with other materials such asarchaeological maps and archaeological documents.

Moreover, the features extracted andestimated by RS/GIS methodologies were veriﬁed by ﬁeld survey conducted by specialists inarchaeology, anthropology and informatics.
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