Ghiyas-ud-Din Tughlaq (1321-25) built the fortified town of Tughlaqabad, the third city of Delhi. With its battered walls of grey rubble perched on desolate hills, where its position gives it a natural advantage, Tughlaqabad was raised as a stronghold rather than as an architectural enterprise. It is in two parts, the citadel and palaces along the southern walls forming one unit and the city to the north the other. On plan it is an irregular rectangle with over 6 km. of fortification. The citadel is still intact, and the walls of palaces can also be discerned. The city-portion is, however, in extreme ruins, although one may make out the alignment of some of its streets.
Across the main entrance of Tughlaqabad on the south is Ghiyas-ud-Din's tomb. Faced with red sandstone relieved by marble, and with batter on exterior, it is enclosed within high walls forming an irregular pentagon. With a 'spear-head' fringe on the underside of its arched openings on three sides and its colour-scheme, it still retains some of the characteristics of Khalji architecture. But its arch, with an ogee curve at the apex recalling the 'Tudor' arch, a slightly-pointed 'Tartar' dome and the use of beam-and-arch for openings are new features.
Originally it stood within an artificial reservoir and was connected with Tughlaqabad by a causeway, now pierced by the Qutb-Badarpur road. The sluice-gates of the vast reservoir are to be seen to the north of the main road close to the massive embankment between the northern and southern spurs of the hills. Ghiyathu'd-Din's successor, Muhammad Tughluq (1325-51), added the small fortress of 'Adilabad on the hill south of Tughluqabad, with which it shares the main characteristics of construction.