 It had a population of 7,000 according to Tang dynasty records.It was finally abandoned after its destruction during an invasion by the Mongols led by Genghis Khan in the 13th century.The ruins were visited by the archaeologist and explorer Aurel Stein, who described "a maze of ruined dwellings and shrines carved out for the most part from the loess soil", but complained that a combination of local farmers' use of the soil and government interference in his activities prevented examination.