Of all the surviving buildings in the old fort complex, the Sher Mandal and the Quila-i-kunha Mosque are notable. The walls of the immense Qila tower down on the road that takes one to Pragati Maidan from the height of 18m, and run on for about 2km. From the recent excavations near this fort, archaeological evidences such as pottery have been found which throws a new light on the existence of the city of Indraprastha at this place in Delhi. The most fascinating buildings, and also one of the few that still survive, in the Purana Qila is the Qila-i-kuhna masjid. Sher Shah Suri built it in 1541 (also see History) and he was obviously out to make a definite style statement. The mosque is quite a place; its prayer hall measures 51.20m by 14.90m and has five doorways with the 'true' horseshoe-shaped arches. Apparently the idea was the build the whole mosque in marble, but the supply ran out and red sandstone had to be used instead. But the builder used the material at hand very skillfully and the result is quite spectacular – the red sandstone and the marble contrast beautifully with each other to give the mosque a very distinctive air. The mihrabs (prayer niches) inside the mosque are richly decorated with concentric arches. From the prayer hall, staircases lead you to the second storey where a narrow passage runs along the rectangular hall. The central alcove is topped by a beautifully worked dome. In the courtyard at one time there was a shallow tank, which had a fountain.