Delhi, known locally as Dilli, and also by the official name National Capital Territory of Delhi (NCT), is the second-largest metropolis in India. With over 15.9 million residents, it is the eighth largest metropolis in the world by population. The name Delhi is often also used to include some urban areas near the NCT, as well as to refer to New Delhi, the capital of India, which lies within the NCT. The NCT is a federally administered union territory.
Located on the banks of the River Yamuna, Delhi has been continuously inhabited since at least the 6th century BC. After the rise of the Delhi Sultanate, Delhi emerged as a major political, cultural and commercial city along the trade routes between northwest India and the Indo-Gangetic plains. It is the site of many ancient and medieval monuments, archaeological sites and remains. In 1639, Mughal emperor Shahjahan built a new walled city in Delhi which served as the capital of the Mughal Empire from 1649 to 1857.