The Archaeological Survey of India has undertaken the most challenging task of conservation and restoration of the Ta Prohm temple complex in Siem Reap, Cambodia within the framework of the international actions for safeguarding and preserving the Angkor World Heritage Site, supported by UNESCO. ASI has adopted a multidisciplinary and integrated approach by including and collaborating with professionals from the fields of archeology, history, epigraphy, structural engineering, hydrology, geology, geo-technology, arboriculture, botany and architecture to understand the complexities of the site and evolve a most appropriate conservation strategy for this monument.

The distinct uniqueness of this temple lies in the remarkable symbiosis between the natural and the built heritage seen here. The forest which has grown and enveloped this temple has created an extraordinary coexistence of the trees and the monument, which needs to be conserved for the future generations. The underlying principle for all the conservation and limited restoration works proposed for Ta Prohm temple is the protection of the authenticity and the integrity of this monument.

This book envisages highlighting the significance of Ta Prohm temple complex and bringing forth the technical studies and investigations undertaken so far. It also focuses upon the proposed implementation plan for the conservation and restoration works to be undertaken by Archaeological Survey of India.

The book comprises of three sections. The first section gives an overview to the temple complex and outlines the various geographical aspects of the site, historical background, architecture of the temple, its significance. It also highlights the issues and challenges in conservation.

The second section gives a detailed account of the technical studies and investigation that have been undertaken which include the structural analysis of the temple, the geotechnical studies, hydrology study, GPR studies and arboriculture studies. Documentation of the temple using the technique of laser scanning has also been discussed.

The third section deals with the conservation strategy and the implementation plan proposed for conservation and restoration of this monument. It discusses in details the proposed structural interventions and drainage system for the site. .

It is my privilege to present this book on Ta Prohm temple as an attempt to provide an overall understanding of the temple-complex and the contribution of Archaeological Survey of India in safeguarding this extremely significant temple complex in the Angkor World Heritage Site.

I owe my thanks to Ministry of External Affairs for all their support and for financing this project. I thank Secretary of Culture, for entrusting this prestigious project to Archaeological Survey of India.

I extend my warm regards to the Cambodian Authorities and to APSARA Authority in particular, for their efforts to ensure the protection of this valuable cultural resource. We look forward to our collaboration and cooperation with APSARA in the efforts to conserve and restore Prasat Ta Prohm complex and to the valuable suggestions of UNESCO experts of the ad-hoc committee in this endeavor.

We are grateful to Dr. Azedine BESCHAOUCH, Special Advisor to DG of UNESCO, Adhoc Panel of Experts of UNESCO Prof. Giorgio CROCI, Prof. Pierre-Andre LABLAUDE, and Dr. Hiroyuki SUZUKI for their valuable suggestions in the Symposium on Ta Prohm, and ICC Technical Committee meetings and during the field visits.

We place on record our deep indebtedness to HE. Mr. Sok AN, Deputy Prime Minister and Chairman of the APSARA Authority for the keen interest he has been evincing in this unique assignment.

We are highly obliged to HE. Mr. Bun Narith, Director General and HE. Mr. Ros Borath, Deputy Director General, Staff and Officers of the APSARA Authority, particularly Ms. Mao Loa, Director, Mr. Ven Sophron, Archaeologist and Mr. Somsoprath, Architect for their valuable suggestions and guidance in addressing the various issues concerning the conservation of this temple complex.

Our thanks are due to Mr. Etienne CLEMENT, UNESCO Representative in Cambodia, Ms. Dominique BALLE CALLIX and Ms. Tamara TENEISHVILI of ICC Secretariat for their invaluable help and guidance.

Our sincere thanks are due to Mr. D.K. Jain, Additional Secretary, MEA, HE. Mr. Aloke Sen the present Indian Ambassador to Cambodia, and HE.. Mr. Pradeep Kapur the former Indian Ambassador in Cambodia for their constant encouragement, guidance and keen interest in the project.

We are extremely grateful to Prof. M.S. Mathews, Prof. and Head of Civil Engineering Dept., Prof. S.R. Gandhi, Prof. and Head of Geotechnical Engineering Division, Prof. Devdas Menon, Prof. and Head of Structural Engg. Division, Prof. Meher Prasad, Prof. of Structural Engg. Division, Prof. Satyanarayana, Prof. of Building Material and Construction Management Division from the Indian Institute of Technology Madras for their studies and investigations pertaining to soil analysis, and structural stability of the various components of the temple.

We are also grateful to Mr. A.D. Mohile, Senior Consultant WAPCOS (Former Chairman CWC), Mr. V.M. Sharma, Geotechnical Engg. and Trenchless technology expert, Dr. Manoj Kumar Verman, GPR expert from Water and Power Consultancy Services (WAPCOS), for their studies and investigations to understand the hydrology of the area and causes for water stagnation in the temple complex.

We are also grateful to Dr. S.S. Negi, Director, Forest Research Institute, Dehradun and Dr. Biswas, Head, Botany Division, FRI, Dehradun, for their arboriculture studies and investigation related to the numerous trees in the temple complex.

We also thank the officials of Laser Scanning Technologies Pvt. Ltd., particularly Mr. Gourango Singha, Application Engineer and Mr. Neil Aschroft, Application Engineer for undertaking the Laser Scanning and documentation of the Ta Prohm temple. We owe our thanks to the officials of Sri Ram Institute for Industrial Research for testing of sandstone samples.

We thank one and all who have been associated with this project.

The archaeologicpl site of Angkor, located in the mainland of Southeast Asia, has fascinated people across the world since its rediscovery in the mid-nineteenth century. The magnificent structures of Angkor represent an unparalleled architectural achievement by the Khmer rulers. The region of Angkor was inscribed in the World Heritage List in 1992. Spread over, an area of 400 sq km, the Angkor World Heritage Site is marked with splendid structures constructed by the Khmer rulers from the ninth to the fifteenth century. The rulers of this Khmer civilization, constructed many temples including the famous temple of Angkor Wat, the royal city of Angkor, palaces, historic water structures, embankments and irrigation canals etc. One such temple is the Buddhist monastic-complex of Ta Prohm constructed in the 12th century. This temple was originally known as Rajavihara (Royal Monastery), later it was given the name of Ta Prohm, Ta means Ancestor, Prohm means Brahma the Hindu God of creation. This temple is of outstanding value and portrays a unique harmonious coexistence of the trees and the built heritage.

The Geographical Context

Ta Prohm Temple is located in Cambodia which is a large depressed basin lying between 102°E and 103°E and 10°N and 15°N covering an area of 181,040 square kilometers. Two thirds of the country is covered by a vast plain. The principal topographical feature is the Mekong River which originates from the Himalayas and flows through the north - east region of Cambodia to the South China Sea. The entire region comprises of three zones, the northern zone, central zone and the southern zone. The northern zone is occupied by the Kulen Mountains. Central zone is an alluvial plain that is occupied by the temple - complexes, moats, reservoirs and canals. The southern zone is the Tonle Sap Lake, which serves as a discharge area for the drainage system and for dispersing water from the temple complexes of the heritage site. The Kulen Mountains in the north zone approximately 20 kms north - east of Angkor averaging a height of 490 m played an important economic, religious and political role in the formation and maintenance of the city of Angkor. These mountains formed the source of water for the canals, moats, reservoirs of the ancient city. The sandstone for the monuments in the region was obtained from the quarries in the Kulen Mountains. It was on these hills that Jayavarman II founded the Khmer Empire in the 9th century. One of the important features of the Cambodian plain is the Tonle Sap Lake. It occupies an area of 2700 square km during the dry season but during the monsoons it expands to occupy an area of 10,360 square km. This is due to the annual reversal of the Tonle Sap River's flow. During the summer monsoons which begin in late May or early June, this river brings the water of the Mekong River back into the flood plain and drowns the low forest that borders the lake. The reverse phenomenon occurs during the winter monsoons in the month of November. The Tonle Sap River changes its direction and the water flows from the Lake towards Phnom Penh and the Delta. This lake varies in depth from 1.5 m to 9.2 m.

Geological Formation

Ta Prohm temple is situated in the Angkor area of Siem Reap, which is part of the Mekong Delta lower lands, that are considered to be of relatively recent geological origin consisting of sedimentary accumulation from the river Mekong and other small rivers. The area is essentially alluvium with extremely high fertility and subjected to frequent flooding, as most of the area is hardly three to four meters above the mean sea level. The central plains, the Mekong-Tonle Sap basin is formed from an ancient marine gulf and later filled with alluvium and colluviums from the Mekong River. The basin periphery comprises of mountain ranges that include a variety of minerals and soil types. This region is flanked by low-lying hills, the sandstone Dangerk Range in the north, Cardamom Range in the southwest and the Elephant Range in the south.

Geo-morphologically, the area is divisible into four distinct regions, which have varied geology and lithology. These are given in Table 1.1. Ta Prohm area is predominated by the alluvial formation. The total thickness of alluvial deposit is 10 to 20 meters in northern area and 20 to 30 meters in the southern area. The diluvium, which is relatively coarser in nature, underlies alluvium and its thickness is around 20 meters.

Hydrology of the Area

The catchment from the mountains in the northern zone forms three rivers Siem Reap, Roulous, and Pouk which drain in the north - south direction (refer to Fig.III). The Siem Reap river and the Sras Sarang pond and the moats are the prime hydrographic features, of this area. The Siem Reap river is the largest perennial river with a catchment area of 670 sq.km which flows through lake Tonle Sap. This river has changed its course and it presently flows on the western side of the Ta Prohm temple complex. The Khmer rulers were extremely sensitive to the hydrology of the area. Location of the capital of the Khmer rulers was such that Angkor was never exposed to floods because it was built at an elevated terrain. Major floods were restricted in the upstream near the North Baray area. The water structures such as, embankments and Barrays were constructed in the east -west direction and they were effective in flood control. The Eastern and Western Baray are two major reservoirs in the Angkor heritage area.

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