About Purana Qila, Delhi
The Purana-Qila (Purana-Qal's) occupies the ancient mound, which conceals perhaps the ruins of the city of Indraprastha of Mahabharata story. Sher Shah Suri demolished the city of Dinpanah built by Humayun and on the same site raised this citadel.
It is irregularly oblong on plan, with bastions on the corners and in the western wall. Its ramparts cover a perimeter of nearly 2-km.and has three main gates on the north, south and west, the last one functioning as the entrance now. The gates are double-storeyed, built with red sandstone and surmounted by chhatris. On the inside, against the enclosure wall run cells in two-bay depth.
Among the three main gates, the northern one is called the 'Talaqi-Darwaza' or the forbidden gate. Why and when the entrance through it was forbidden is not known. Above the oriel windows on its front are carved marble leogryphs engaged in combat with a man. The exterior of the gate was originally decorated with coloured tiles, and the rooms with incised plasterwork.
Legend Of Old Fort
It is believed that Sher Shah left the Purana-Qila unfinished, and Humayun completed it. Among the scribblings in ink that existed in a recess of the gate, there was a mention of Humayun, and it is possible, therefore, that if the gate was not constructed by Humayun, it was at least repaired by him. In the southern gate, which is called the Humayun-Darwaza, there existed a similar inscription in ink mentioning Sher Shah and the date 950 A.H. (1543-44).
Purana-Qila originally lay on the bank of the Yamuna. The general depression on the northern and western sides of the fortress suggests that a wide moat connected with the river existed on these sides, which were approached through a causeway connecting the fortress with the main land.