The main point of Qutb Minar, of course, is the pillar itself, variously speculated on as a minaret for calling the faithful to prayer, a victory tower proclaiming the victory of Islam over Hinduism, or a watch tower for defense. It's exquisite, whatever its purpose:
Ala-ud-din Khilji started building the Alai Minar, below, and intended it to be two times higher than the Qutb Minar. Construction was abandoned, just after the completion of the first story core, shortly after Ala-ud-din's death in 1316 CE, and never taken up by his successors. This core would have been covered by dressed stone eventually.