Koh Ker is situated between the southern slopes of the Dangrek mountains, the Kulen mountains (Phnom Kulen) in the south-west, and 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 .(pp13-14) 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.(p9)