Oudong is a town in Cambodia, situated in the north-western part of Kampong Speu Province. Located at the foothill of the mountain Phnom Udong, about 40 km northwest of the modern capital Phnom Penh, Oudong was royal residence and Cambodia's capital for more than 250 years until 1866. A monumental royal necropolis of sovereigns of several centuries is scattered on top the prominent bisected mountain, which runs from the southeast to the northeast.