Explanation:

Delhi, has seen the rise and fall of many empires which have left behind a plethora of monuments that the grandeur and glory of bygone ages . A city which traces its history to Mahabharata, the great epic tale of wars fought between estranged cousins , the Kauravas and the Pandavas for the city of Indraprastha.
It is popularly said that Delhi was the site for a total of seven different cities between 3000 B.C. and the 17th century A.D., although taking smaller towns and strongholds into account, as many as 15 settlements can be identified. All the earlier locations of Delhi fall within an area commonly called the 'Delhi Triangle,' bounded on the south and the west by the Aravalli Range, known as the Delhi Ridge, and to the east by the Yamuna River.[6][7]
Notable settlements to have been established in the region include:[6][7]
•    Indraprastha, supposedly built by the Pandavas.
•    Surajkund (Anangpur), Tomar-Gurjar city dating from the 9th or 10th century, where a large masonry tank can be found.
•    Lalkot, built ca. 1052 A.D. by the Tomara ruler, Anangpal. In ca. 1180 A.D. Prithviraj Chauhan extended and fortified it as a defence against Muslim invaders; the city then became known as Qila Rai Pithora. This area, now called as Mehrauli, was also the seat of the Mamluk (Slave) dynasty.
•    Siri, first established as a camp for protection against invading Mongols by Alauddin Khilji, and fortified in about ca. 1303 A.D.
•    Tughluqabad, built by Ghiyasuddin Tughluq in ca. 1320 A.D. A subsidiary fort Adilabad was built by his son Muhammad bin Tughlaq in ca. 1325 A.D.Presently tanwar and dedha gurjar
•    Jahanpanah, Refuge of the World, name given to the area enclosed by walling-in of the suburbs between Qila Rai Pithora and Siri, built by Muhammad bin Tughluq in ca. 1325 A.D.
•    Ferozabad, built by Firuz Shah Tughluq in ca. 1354 A.D.; all that remains is the palace, known as Feroz Shah Kotla. Feroz Shah’s building activity indicates that the suburbs were still occupied; major mosques were built inside Jahanpanah (Khirki and Begumpur) and Nizamuddin[disambiguation needed]; and the area around Khilji reservoir Hauz Khas was developed.
•    Dinpanah built by Humayun and Shergarh built by Sher Shah Suri, both in the area near the speculated site of the legendary Indraprastha (1538–1545).
•    Shahjahanabad, the walled city built by Shah Jahan from 1638 to 1649, containing the Lal Qila and the Chandni Chowk. It was the capital of the Mughal Empire during Shah Jahan's reign. It is presently referred to as "Old Delhi".
•    Lutyens' Delhi or New Delhi, the city built by the British on the south-west, declared Capital on 12 December 1911. On 12 December 2011 New Delhi celebrated 100 years of serving as India's National Capital.[8]
Modern Delhi, referred to as 'Dilli' locally, derived from its historical name Dhili, is an amalgam all of the above. Officially, however, only seven of the above-mentioned settlements are recognised.[9]as historical cites with distinct identities and indigenous heritage: Qila Rai Pithora, Mehrauli, Siri, Tughlaqabad, Ferozabad, Dinpanah and Shahjahanabad.
The rest are not officially identified as Cities of Delhi because of some specific reasons.
•    Indraprastha, the legendary Ancient City is believed to have been established 5000 years ago (c. 2800 BC), as per the ancient Indian text- the Mahabharata. Though very much a part of India's very Ancient history, it lacks any tangible evidence to say without doubt that it existed. Archaeological evidence exists, but in such scarcity as be inconclusive. As acknowledged by British historian Michael Wood in his BBC documentary The Story of India,[10] the excavated ceramic pottery from the site of today's Purana Qila in Delhi and the excavated layers of the ancient city seem to match what the verses of the Mahabharata indicate. More possible evidence in its favour is the existence of a village named Indraprastha very close to the Purana Qila that was destroyed by the British during the construction of Lutyens' Delhi.[11]
•    Jahanpanah is not considered as a City of Delhi because it is very much in ruins and too diffused now to be considered a distinct city. Moreover, sections of the city still standing are now counted in Siri or Mehrauli-Gurjar.
•    Lodi Complex is not counted as a distinct city because their architectures are too few to be counted as a whole city. The Sayyid and Lodhi dynasties that followed the Tughlak dynasty were far more concerned with restoring stability than patronisation of arts or architecture. Tombs erected in the honour of the rulers are the only monuments of these times and these are scattered all over current South and Central Delhis.[12]
•    New Delhi, the Capital city of modern India is also not counted as a City of Delhi because the structures of those times are still in use as government buildings. So there seems no such thing as "history" about it.

Mughals ruled Delhi in succession starting from Qutab-ub-din to Khiljis, Tughlaqs . The city of Delhi passed on to the hands of the British in 1803 AD. It was only in 1911, when the capital of British empire was shifted from Calcutta to Delhi, that Delhi got its present prestige. After independence also, a kind of autonomy was conferred on the capital but it largely remained a chief commissioners regime. In 1956 Delhi was converted into a Union territory and gradually the chief commissioner was replaced by a Lt. Governor. In 1991, the national capital territory Act was passed by the parliament and a system of diarchy was introduced under which, the elected Government was given wide powers; except law and order which remained with the central Government. The actual enforcement of the legislation came in 1993.