Delhi is a metropolitan region in India. With a population of 22 million in 2011, it is the world's second most populous city and the largest city in India in terms of area. The NCR includes the neighbouring cities of Alwar, Baghpat, Gurgaon, Sonepat, Faridabad, Ghaziabad, Noida, Greater Noida and other nearby towns, and has nearly 22.2 million residents. Through most of its history, Delhi has served as a capital of various kingdoms and empires. It has been captured, ransacked and rebuilt several times, particularly during the medieval period, and the modern Delhi is a cluster of a number of cities spread across the metropolitan region.