In 1638 Shahjahan transferred his capital from 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, some of which 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 begun in 1639 and completed after nine years. The Red Fort is different from the Agra fort and is better 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 Lahori and Delhi gates respectively. While the walls, gates and a few other structures in the fort are constructed of red sandstone, marble has been largely used in the palaces. Emperor Shah Jahaan’s royal seat stood in Diwan-i-Khas (Hall of Private Audience), made of solid gold frame and studded with precious stones such as rubies, emeralds, pearls and diamonds including the world’s largest, the Kohinoor.

The Red Fort was the residence of the Mughal emperors of India for nearly 200 years, until 1857. With the end of the Mughal reign, the British gave official sanctions to remove and sell valuables from the palace at the Red Fort. In 1863, British destroyed many buildings inside and outside the fort, filled up the gardens, stripped the fort of any valuable items and reduced the fort to just a military structure.

On 15 August 1947, the first Prime Minister of India Jawaharlal Nehru raised the Indian national flag above the Lahore Gate. On each subsequent Independence Day, the prime minister has raised the flag and given a speech that is broadcast nationally.

Reference:

http://www.indianage.com/search.php

http://asi.nic.in/asi_monu_tktd_delhi_redfort.asp

http://en.wikipedia.org/wiki/Red_Fort

http://www.indiatvnews.com/news/india/top-10-interesting-facts-about-red-fort-26406.html