The Alai Darwaza, the southern gateway of the Quwwat-ul-Islam mosque, was built mainly of:

The Alai Darwaza, built by Alauddin Khalji in 1311 CE, is made mainly of red sandstone, decorated with white marble inlay and carvings.

About the Alai Darwaza:

• It is located in the Qutub complex in Mehrauli, Delhi.
• It was built as the southern gateway of the Quwwat-ul-Islam mosque, which Alauddin enlarged.
• It is a square building with a dome, with arched entrances on all four sides.

Architectural importance:

• It is regarded as the first building in India to use the true dome built according to Islamic (Seljuk) principles.
• Its pointed "horseshoe" arches are among the earliest true arches in India, built with voussoirs (wedge-shaped stones).
• The arches have a fringe of "spearheads" (lotus buds) along the edges.
• It uses the system of "squinches" (arches across the corners) to support the dome on a square base.
• It shows the influence of Seljuk architecture from Central Asia and Persia.

Decoration:

• The red sandstone surface is decorated with bands of white marble inlay, geometric patterns, and carved Arabic inscriptions (in Naskh script).
• The use of red and white stones together became a feature of later Indo-Islamic architecture, including Mughal buildings.

Historians on the building:

• Historians regard it as one of the finest gems of early Indo-Islamic architecture.
• It marks an important step in the development of Indo-Islamic architecture, from the earlier "corbelled" (false) arches to true arches and domes.

Other buildings in the Qutub complex:

• The Quwwat-ul-Islam mosque.
• The Qutub Minar.
• The Iron Pillar of Mehrauli (Gupta period).
• The tomb of Iltutmish.
• The incomplete Alai Minar.
• The Qutub complex is a UNESCO World Heritage Site.

Earlier true arch:

The tomb of Balban, built earlier, is believed to have the first true arch in India.

Why not the other options?

• ✗Grey granite, white marble only and burnt brick are not the main materials of the Alai Darwaza.