Purana Quila or Old fort, was built by the great Afghan ruler Sher Shah Suri, in the 16th century A.D. It is situated in Delhi.

The structure houses a mosque, which has a double-storeyed octagonal tower. Recent excavations at the fort site have yielded painted grey ware pottery, which dates back to 1000 B.C. The walls of the fort are 18 meters high at some points and there are groups of holes arranged in patterns on the walls, which were apparently meant to be nesting spaces for birds.

Inside the fort is the Kuhna Masjid built by Sher Shah in 1541 and is considered to be a masterpiece of architecture. The inner west wall of the building has five arched openings, which are richly ornamented in white and black marble. On a marble slab inside the mosque is an inscription which when translated reads: ' as long as there are people on this earth, may this edifice be frequented and people be cheerful and happy in it'.

Out of the three gigantic entrance gateways (Humayun Darwaza, Talaqi Darwaza and Bara Darwaza) that Purana Qila had, only one remains open now, the Bara Darwaza. The central section of the mosque made up of white marble and bright red sandstone gives it a real touch of class.