Quwwat-ul-Islam mosque (Might of Islam) (also known as the Qutub Mosque or the Great Mosque of Delhi) was built by Qutb-ud-din Aibak, founder of the Mamluk or Slave dynasty. It was the first mosque built in Delhi after the Islamic conquest of India and the oldest surviving example of Ghurids architecture in Indian subcontinent. The construction of this Jami Masjid (Friday Mosque), started in the year 1193 AD, when Aibak was the commander of Muhammad Ghori's garrison that occupied Delhi.
The Qutub Minar was built simultaneously with the mosque but appears to be a stand alone structure, built as the 'Minar of Jami Masjid', for the muezzin to perform adhan, call for prayer, and also as a qutub, an Axis or Pole of Islam. It is reminiscent in style and design of the Arhai-din-ka Jhompra or Ajmer mosque at Ajmer, Rajasthan, also built by Aibak during the same time, also constructed by demolishing earlier temples and a Sanskrit school, at the site.
According to a Persian inscription still on the inner eastern gateway, the mosque was built by the parts taken by destruction of twenty-seven Hindu and Jain temples built previously during Tomars and Prithvi Raj Chauhan, and leaving certain parts of the temple outside the mosque proper. Historical records compiled by Muslim historian Maulana Hakim Saiyid Abdul Hai attest to the iconoclasm of Qutb-ud-din Aybak. This pattern of iconoclasm was common during his reign, although an argument goes that such iconoclasm was motivated more by politics than by religion.
The mosque is built on a raised and paved courtyard, measuring 141 ft (43 m). X 105 ft (32 m), surrounded by pillared cloisters added by Iltutmish between 1210 and 1220 AD. The stone screen between prayer hall and the courtyard, stood 16 mt at its highest was added in 1196 AD, the corbelled arches had Arabic inscriptions and motifs. Entrances to the courtyard, also uses ornate mandap dome from temples, whose pillars are used extensively throughout the edifice, and in the sanctuary beyond the tall arched screens.
What survives today of the sanctuary on the western side are the arched screens in between, which once led to a series of aisles with low-domed ceilings for worshippers. Expansion of the mosque continued after the death of Qutb. Qutbuddin's successor Iltutmish, extended the original prayer hall screen by three more arches. By the time of Iltutmish, the Mamluk empire had stabilized enough that the Sultan could replace most of his conscripted Hindu masons with Muslims.
This explains why the arches added under Iltutmish are stylistically more Islamic than the ones erected under Qutb's rule, also because the material used wasn't from demolished temples. Some additions to the mosque were also done by Alauddin Khilji, including the Alai Darwaza, the formal entrance to the mosque in red sandstone and white marble, and a court to the east of the mosque in 1300 AD.
The mosque is in ruins today but indigenous corbelled arches, floral motifs, and geometric patterns can be seen among the Islamic architectural structures. To the west of the Quwwat ul-Islam mosque is the tomb of Iltutmish which was built by the monarch in 1235.