Delhi, officially the National Capital Territory of Delhi (NCT), is a city and a union territory of India. It is bordered by Haryana on three sides and by Uttar Pradesh to the east. The NCT covers an area of 1,484 square kilometres (573 sq mi). According to 2011 census, Delhi’s city proper population was over 11 million, the second highest in India after Mumbai, while the whole NCT’s population was about 16.8 million. Delhi’s urban area is now considered to extend beyond the NCT boundary to include an estimated population of over 26 million people, making it the world’s second largest urban area. As of 2016 recent estimates of the metro economy of its urban area have ranked Delhi either the top or second most productive metro area of India. Delhi is the second wealthiest city after Mumbai in India, with a total wealth of $450 billion and home to 18 billionaires and 23,000 millionaires.
There are a number of myths and legends associated with the origin of the name Delhi. One of them is derived from Dhillu or Dilu, a king who built a city at this location in 50 BC and named it after himself. Another legend holds that the name of the city is based on the Hindi/Prakrit word dhili (loose) and that it was used by the Tomaras to refer to the city because the Iron Pillar of Delhi had a weak foundation and had to be moved. The coins in circulation in the region under the Tomaras were called dehliwal. According to the Bhavishya Purana, King Prithiviraja of Indraprastha built a new fort in the modern-day Purana Qila area for the convenience of all four castes in his kingdom. He ordered the construction of a gateway to the fort and later named the fort dehali. Some historians believe that the name is derived from Dilli, a corruption of the Hindustani words dehleez or dehali—both terms meaning ‘threshold’ or ‘gateway’—and symbolic of the city as a gateway to the Gangetic Plain. Another theory suggests that the city’s original name was Dhillika.