Damghan (Persian: , romanized: Dmghn) 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 km (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 7,000 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 Sasanian Empire.

The Tarikhaneh is one of the oldest mosques in Iran, built as a fire temple during the Sassanid dynasty, it was converted into a mosque after the advent of Islam. There are also many other historical buildings belonging to the Seljuk Empire and other periods. Apart from its historical interest, the city today is mainly known for pistachios and paper almonds (kaghazi) with very thin shells.

The 856 Damghan earthquake or the 856 Qumis earthquake occurred on 22 December 856 (242 AH). The earthquake had an estimated magnitude of 7.9, and a maximum intensity of X (Extreme) on the Mercalli intensity scale. The meizoseismal area (area of maximum damage) extended for about 350 kilometres (220 mi) along the southern edge of the eastern Alborz mountains of present-day Iran including parts of Tabaristan and Gorgan. The earthquake's epicenter is estimated to be close to the city of Damghan, which was then the capital of the Persian province of Qumis. It caused approximately 200,000 deaths and is listed by the USGS as the sixth deadliest earthquake in recorded history. This death toll has been debated.