Damghan is the capital of Damghan County, Semnan Province, Iran. At the 2006 census, its population was 57,331, in 15,849 families. It is situated 342 kilometres (213 mi) east of Tehran on the high-road to Mashad, at an elevation of 1,250 m (4,101 ft). It is one of the oldest cities on the Iranian plateau, stretching back 7000 years, and boasts many sites of historic interest. The oldest of these is Tappeh Hessar, lying to the southeast of the city, which holds the ruins of a castle dating from the Sassanid period.