This famous gate, Alai Darwaaza, is about 12 meters south-east of Qutb Minar. It was built by Ala-ud-din Khilji in 1311 as the southern gate to the Qutb Mosque extended by him. The building is rather small, for, it is only 17.3 meters square externally with an internal apartment only 10.5 meters in plan.
Alai Darwaza marks the zenith of the early Indo-Muslim style of architecture. Cunningham declared it to be “the most beautiful specimen of Pathan architecture” ever seen by him, and Fergusson remarked that “it displays the Pathan style at its period of greatest perfection, when the Hindu masons had learned to fit their exquisite style of decorating to the forms of their foreign master. The Alai Darwaza is indeed a gem of Indo-Islamic architecture on account of its well-built horse-shoe arches, its wealth of lace-like pleasing decoration on the exterior, its well-proportioned lineaments and its pleasing effect due to use of red sandstone and marble.