Alai Darwaza (Urdu: علاء دروازہ, literally "Gate of Alauddin") is the southern gate of the Quwwat-ul-Islam Mosque in the Qutb complex, Mehrauli, Delhi, India. Built by Sultan Alauddin Khilji in 1311 from red sandstone, it is a square domed structure with arched entrances and a single hall. Alai Darwaza holds special significance in Indo-Islamic architecture as it is the first Indian monument constructed using Islamic building and decoration techniques and is a UNESCO World Heritage Site.

Alai Darwaza was built by the Delhi Sultan Alauddin Khilji of the Khilji dynasty in 1311. It was part of his plan to expand the Quwwat-ul-Islam Mosque on all four sides. Although he intended to build four gates, only the Alai Darwaza was completed, as he died in 1316. It serves as the southern gate of the mosque and is located in the southern part of the Qutb complex.

In 1993, Alai Darwaza and other monuments of the complex were included in the list of World Heritage Sites. The surroundings of the Qutb Minar, which include numerous tombs, mosques, and the Iron Pillar, are called the Qutb complex. Alai Darwaza consists of a single hall with internal dimensions of 10.5 meters and external dimensions of 17.2 meters. The height of the structure is 18 meters, and the walls are 3.4 meters thick.

The gate, built in 1311, still demonstrates a cautious approach to new technology, with very thick walls and a shallow dome that is visible only from a certain distance or height. The contrasting colors of the masonry, with red sandstone and white marble, introduce what became a common element of Indo-Islamic architecture, replacing the polychrome tiles used in Persia and Central Asia. The pointed arches slightly converge at the base, creating a soft horseshoe arch effect, and their inner edges are not framed but laid out with traditional "spearhead" projections, possibly representing lotus buds. Stone carved screens, which had long been used in temples, are introduced here.

The height of the dome is 14 meters. This is the first true dome built in India, as previous attempts to construct a true dome had not been successful.

The entire Darwaza is built from red sandstone with white marble inlaid on the outer walls. There is extensive Arabic calligraphy on the walls of the Darwaza. The arches have a horseshoe shape, the first time such arches were used in India. The facade is decorated with pre-Turkish carvings and patterns. The windows have marble lattices. Surface decorations consist of intertwined floral scrolls symmetrically repeated on the three door openings.

Sources:

https://en.wikipedia.org/wiki/Alai_Darwaza