Alai Minar
Alauddin Khilji started building the Alai Minar, after he had doubled the size of Quwwat ul-Islam mosque. He conceived this tower to be two times higher than Qutb Minar in proportion with the enlarged mosque. The construction was however abandoned, just after the completion of the 24.5-metre-high (80 ft) first-storey core; soon after death of Ala-ud-din in 1316, and never taken up by his successors of Khilji dynasty. The first storey of the Alai Minar, a giant rubble masonry core, still stands today, which was evidently intended to be covered with dressed stone later on. Noted Sufi poet and saint of his times, Amir Khusro in his work, Tarikh-i-Alai, mentions Ala-ud-din's intentions to extend the mosque and also constructing another minar.
Ala-ud-din conceived a very ambitious construction programme when he decided to build the second tower of victory when he returned in triumph from his Deccan campaign. However, the Sultan died before even the first storey was finished, and the project was abandoned. Ala-ud-din felt compelled to increase even further the size of the Quwwat-ul-Islam mosque. His scheme called for increasing the size of the enclosure four times, providing ceremonial entrance gateways on each side, and a great minar, twice the size of the Qutb. This is the unfinished base of the mammoth tower begun by Ala-ud-din Khilji intended to give competition to Qutb Minar.
Read more about this topic: Qutb Complex