Previous archaeological mapping work on the successive medieval capitals of the Khmer Empire located at Angkor, in northwest Cambodia (∼9th to 15th centuries in the Common Era, C.E.), has identified it as the largest settlement complex of the preindustrial world, and yet crucial areas have remained unmapped, in particular the ceremonial centers and their surroundings, where dense forest obscures the traces of the civilization that typically remain in evidence in surface topography. Here we describe the use of airborne laser scanning (lidar) technology to create high-precision digital elevation models of the ground surface beneath the vegetation cover. We identify an entire, previously undocumented, formally planned urban landscape into which the major temples such as Angkor Wat were integrated. Beyond these newly identified urban landscapes, the lidar data reveal anthropogenic changes to the landscape on a vast scale and lend further weight to an emerging consensus that infrastructural complexity, unsustainable modes of subsistence, and climate variation were crucial factors in the decline of the classical Khmer civilization.Southeast Asia | urbanism | sustainability | resilience | water management

The Angkor monuments in Cambodia are mainly constructed of grey to yellowish‐brown sandstones. No differences in the constituent minerals and in the chemical composition of the sandstones have been confirmed among the monuments. However, we have found their magnetic susceptibility a useful parameter by which to distinguish them. The principal monuments of Angkor Wat, Ta Prohm, Preah Khan, Banteay Kdei and Bayon, constructed from the Angkor Wat period to the Bayon period (from the beginning of the 12th century to the beginning of the 13th century ad), were investigated in detail using a portable magnetic susceptibility meter. We succeeded in dividing the periods of construction into stages. This elucidated the enlargement process of the monuments and correlated their construction stages.

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Annual change in the density of sulfur-oxidizing microorganisms on sandstone was enumerated to know the effects on the deterioration of stone materials of the Angkor monuments in Cambodia. Samples were obtained from total 12 stations at the Angkor Wat, Bayon, and Phnom Krom temples between 1998 and 2007. Sulfur-oxidizing microorganisms enumerated in a mineral salts medium supplemented with elemental sulfur as the sole energy source had a density of 10 1 -10 5 MPN (g sample) −1 . The sulfur-oxidizing microorganisms of the samples collected at Angkor Wat have tended to decrease in density since 2002; on the other hand, relatively constant values have been recorded in the samples of Bayon and Phnom Krom. These results suggest that the sulfur-oxidizing microorganisms on the stone play an important role in the decay of the building blocks by excreting sulfuric acid.

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