Firoz Shah Kotla , the citadel of Delhi's sixth city, Firozabad, is entered from the gate beside the Khooni Darwaza. Firoz Shah, the third Tughlaq sultan to rule Delhi (1351-88), was like Shah Jahan, who would follow him three centuries later, an enthusiastic builder, but he appears to have had limited funds available, as much of his city consisted of restored structures, and plastered rubble predominated over sandstone. Nevertheless, Firozabad covered a large area, which comprised most of Old Delhi. It is said that some secret passages led from the citadel to the river, the North Ridge hunting lodge and a location near the Qutub Minar in south Delhi, where Firoz Shah is buried. Timur defeated the last Tughlaq ruler of Delhi, Nasir-ud-din Tughlaq, in 1398 and some of his troops were killed attempting to collect ransom from the citizens. In revenge, Timur slaughtered 3,000 inhabitants of Firozabad and razed the city to the ground. The ruins would later serve as building material for the cities of Shergarh and Shahjahnabad.
Nothing of Firozabad survives apart from this citadel palace, which was built, possibly for the first time in Delhi, on the west bank of the river. Much later construction makes it difficult to appreciate the original layout of the complex, which consisted of three separate enclosures. Nevertheless, its Ashoka pillar and mosque are important Delhi monuments.