In 1638 shahjahan transferred his capital to agra to delhi and laid the foundations of shahjahanabad, the seventh city of delhi. it is enclosed by a rubble stone wall, with bastions, gates and wickets at intervals. of its fourteen gates, the important ones are the mori, lahori, ajmeri, turkman, kashmiri and delhi gates, of which some have already been demolished. his famous citadel, the lal-qila, or the red fort, lying at the town's northern end on the right bank or the yamuna and south of salimgarh, was started in 1639 and completed after nine years. the red fort is different from the agra fort and is well planned, because at its back lies the experience gained by shahjahan at agra, and because it was the work of one hand. it is an irregular octagon, with two long sides on the east and west, and with two main gates, one on the west and the other on the south, called lahohi and delhi gateways respectively. while the walls, gates and some other structures in the fort are made of red sandstone, marble has been largely used in the palaces.