Shah Jahan shifted his capital from Agra to Shahjahanabad and laid the foundation of Red Fort, or the Lal Quila, on 16th April 1639. It took nine years to build this mighty citadel and it got completed on 16th April 1648. It is said that about one crore rupees, an astronomical sum in those days, was spent on its construction. Half of this sum was spent to build the exotic palaces within the fort. Built of red sandstone, it is octagonal in shape, with two longer sides on the east and west.

The perimeter of its strong ramparts is about 2.41 km. Red Fort rises to a height of 33.5 m on the town side and 18 m along the river. A wide moat surrounds the fort, which was originally connected with the river and was always filled with water. The two main gateways, known as Lahori Gate and Delhi Gate (named so, as they face Lahore and Delhi respectively), are three storeys high and are flanked by semi-octagonal towers. They are situated on the centre of the western and southern sides respectively.

The main entrance to the Lal Quila is through the Lahori Gate. Beyond the gate, there is a roofed passage, flanked by arcaded apartments leading to the palaces, known as Chhatta Chowk. These apartments are now used as shops. Besides these, there are three more gates on other sides, which are kept closed now. The master builders of the Red Fort were Hamid and Ahmad.