After transferring his capital to Delhi from Agra in 1638, Shah Jahan commenced the construction of Shahjahanabad, and a little later, on the 16th April, 1639, he also laid the foundation of his citadel, Lal-Qila or Red Fort, known also by other names in contemporary accounts. It was completed after nine years on the 16th April 1648. The entire fort is said to have cost about one crore of rupees, half of it on the palaces.

The Red Fort, so called because of the red colour of the stone largely used in it, is octagonal on plan, with two longer sides on the east and west. The fort measures about 900 m by 550 m, with its rampart walls covering a perimeter of 2.41 km and rising to a height of 33.5 m on the town side and 18 m on along the river. Outside the ramparts runs a moat, originally connected with the river. On the north the fort is connected by a bridge with Salimgarh.

The palaces lie along the eastern side of the fort, while two imposing three-storeyed main gateways flanked by semi-octagonal towers and consisting of several apartments are located in the centre of the western and southern sides and are known as the Lahore and Delhi Gates respectively. On the outside, the Delhi gate is flanked by the statues of two elephants renewed in 1903 by Lord Curzon in place of the ones which had been demolished long ago by Aurangzeb.

The main entrance to the fort lies through the Lahori Gate and the palaces are reached through a roofed passage, flanked by arcaded apartments called Chhatta-Chowk and now used as shops. The other portions were originally occupied by the residences of the courtiers and retinue. Both the ages were provided later by barbicans by Aurangzeb. There exist three other entrances on other sides, now largely closed.

The master-builders of the Red Fort were Hamid and Ahmad while the construction was supervised by other officers, who were amply rewarded by the emperor by appointing them to high positions.