Question

What features of delhi made it the preferred location of medieval rulers?

Answer 1

A variety of cities around in the Gangetic river valley have been major capitals. Patna along the Ganges was the greatest of all with the Mauryas and Guptas coming out of them. A little upstream of that is the Gaya, the enlightenment place for Buddha. If you go further upstream, you can find the great cities of Allahabad, Varanasi, Kannauj and Kanpur that have all been capital of various kingdoms. If you go along the Yamuna, you can again find the ancient capitals of Agra, Mathura, Ujjain (on the tributary river Shipra) and Delhi.

For a lot of invading powers, Delhi was convenient as it was close enough to the Gangetic plains without going too far into India. They could still keep their ties to central Asia from Delhi. Other ancient invaders like the Kushans too kept their capitals much more upstream - in Mathura. 

Then there were two key events that made Delhi stand out from other Gangetic valley capitals. First was the decision by Shah Jahan to build the city of Shahjahanabad - now called Old Delhi and move the capital of Mughal empire from Agra. That was a major decision that allowed Mughals to move closer to the centre of North India and Delhi stayed as the Mughal capital for the next couple of centuries. 

The successors of Mughals, British Empire, initially stayed off Delhi and by 1911 it was yet another dusted Mughal town. However, the rising nationalism in Bengal forced them to move substantially upstream - from near the mouths of Ganges in Calcutta to Delhi. British, like other Indian invaders, found the Gangetic plains too nationalist for their needs forcing them to move upstream.

Answer 2

Explanation:

Pointed arched in the Muslim structures:

Besides arches, they also used domes over their buildings and minarets on sides. The use of arch and dome added charm to the Muslim buildings and also enabled them to dispense with the need of a large number of pillars to support the roof.