 It stood in one location (Khoshoo Tsaidam) for an unusually long period of 15 years from 1640 to 1654 before Zanabazar moved it east to the foot of Mount Saridag in the Khentii Mountains.Here he set about building a permanent monastery town with stone buildings.Urga stayed at Mount Saridag for a full 35 years and was indeed assumed to be permanent there when Oirats suddenly invaded the region in 1688 and burnt down the city.