the Tbeng mountain (Phnom Tbeng, near Tbeng Meanchey) in the east. Most parts of the hilly ground are covered by jungle, but most of the trees shed their leaves seasonally. The city of Koh Ker was on the most important strategic route of the Khmer empire. Coming from Angkor and Beng Mealea to Koh Ker this road led to Prasat Preah Vihear and from there to Phimai in Thailand and Wat Phu in Laos . The region of Koh Ker is relatively dry. Numerous water-tanks and canals were built during the 9th and the 10th century to ensure the water supply. These days water is pumped up from a depth of meters. History Jayavarman IV Jayavarman IV ruled from 928 to 941 at Koh Ker. He was a believed to have been the local king at this remote site, possibly his homeland, before he became king of the whole empire. That could explain why he had his residence at Koh Ker and not at Roluos (Hariharalaya) or at Yashodharapura (Angkor) like the kings before him. Some historians think that Jayavarman IV was an usurper; but, the majority of them believe that he was a legitimate ruler who could ascend to the throne because he married a half-sister of king Yasovarman I (889 – 900). What is certain is that the two sons of Yasovarman I (Harshavarman I, who ruled from 900 to 922 and Isanavarman II, who ruled from 922 to 925?) had no children. In the short time that Jayavarman IV reigned in Koh Ker, an ambitious building program was realised. That was only possible because of a restrictive system of raising taxes as seen on inscriptions found at the site. About 40 temples, the unique seven-tiered pyramid and a huge baray (water-reservoir) were built. Under Jayavarman IV, the Koh Ker-style was developed and the art of sculpture reached a pinnacle. Harshavarman II After the death of Jayavarman IV, the designated prince did not take his place. Harshavarman II (another son of Jayavarman IV) claimed the throne. Like his father, he ruled at Koh Ker (941 – 944) but after three years he died; likely not due to natural causes. None of the temples at Koh Ker can be ascribed to him. His follower on the throne, a cousin of his, returned Roluos (Hariharalaya) to the seat of power. Koh Ker after 944 AD Even after 944, as the