 By 22 July, the troops camped under the wall of another fortress, Peté Jong, deserted and in ruins, while Mounted Infantry pushed on ahead to seize the crossing at Chushul Chakzam, the Iron Bridge.On 25 July, the army began to cross the Tsangpo in the wake of the Mounted Infantry, a feat that took four days to achieve.The force arrived in Lhasa on 3 August 1904 to discover that the thirteenth Dalai Lama had fled to Urga, the capital of Outer Mongolia.