Delhi is one of the oldest continually inhabited cities in the world. Having been the capital of several empires in ancient India, Delhi was a major city in the old trade routes from northwest India to the Gangetic Plains. Many ancient monuments, archaeological sites and remains of national importance have been erected in its history. The Mughals built a section of the city (now known as Old City or Old Delhi) that served as the capital of Mughal Empire for a long period. During the British Raj, New Delhi was built as an administrative quarter of the city. New Delhi was declared the capital of India after India gained independence from British rule in 1947. As the seat of the Government of India, New Delhi houses important offices of the federal government, including the Parliament of India. Delhi has grown up to be a cosmopolitan city owing to the immigration of people from across the country. Like many other large cities of the world, Delhi suffers from urbanisation problems such as pollution, traffic congestion and scarcity of resources. The rapid development and urbanisation of New Delhi and surrounding areas coupled with the high average income of the populace has largely eclipsed socio-cultural traits that used to represent Delhi until a few years after independence.
Human habitation was probably present in and around Delhi during the second millennium BCE and before, as evidenced by archeological relics. The city is believed to be the site of Indraprastha, legendary capital of the Pandavas in the Indian epic Mahabharata. Settlements grew from the time of the Mauryan Empire (c. 300 BC). Remains of seven major cities have been discovered in Delhi. The Tomara Rajput dynasty founded the city of Lal Kot in 736 AD. The Chauhan Rajput kings of Ajmer conquered Lal Kot in 1180 AD and renamed it Qila Rai Pithora. The Chauhan king Prithviraj III was defeated in 1192 by the Afghan Muhammad Ghori. In 1206, Qutb-ud-din Aybak, the first ruler of the Slave Dynasty established the Delhi Sultanate. Qutb-ud-din started the construction the Qutub Minar and Quwwat-al-Islam (might of Islam), the earliest extant mosque in India. After the fall of the Slave dynasty, a succession of Turkic and Central Asian dynasties, the Khilji dynasty, the Tughluq dynasty, the Sayyid dynasty and the Lodhi dynasty held power in the late medieval period, and built a sequence of forts and townships that are part of the seven cities of Delhi. (Source-Wikipedia.org)