Q: Context: The Tomb of Ghiyas ud din Balban is located in Mehrauli, New Delhi, India. Built in circa 1287 CE in rubble masonry, the tomb is a building of historical importance in the development of Indo-Islamic architecture, as it was here that first true arch made its appearance in India, and according to many, the first true dome as well, which however has n't survived, making Alai Darwaza built in 1311 CE, in the nearby Qutb complex, the earliest surviving true dome in India. Ghiyas ud din Balban (1200 -- 1287) was a Turkic ruler of the Delhi Sultanate during the rule of Mamluk dynasty of Delhi (or Slave dynasty) from 1266 to 1287. He was one of the most prominent rulers of the Slave Dynasty. The tomb of Balban was discovered in the mid-twentieth century.

Question: the earliest surviving building in india containing a true dome is?
Let's give stream of consciousness below
The relevant sentence in the passage is: Built in circa 1287 CE in rubble masonry, the tomb is a building of historical importance in the development of Indo-Islamic architecture, as it was here that first true arch made its appearance in India, and according to many, the first true dome as well, which however has n't survived, making Alai Darwaza built in 1311 CE, in the nearby Qutb complex, the earliest surviving true dome in India. So the answer is Alai Darwaza.