Abuja is the capital city of Nigeria. It is located in the centre of Nigeria, within the Federal Capital Territory (FCT). Abuja is a planned city, and was built mainly in the 1980s. It officially became Nigeria's capital on 12 December 1991, replacing Lagos, which is still the country's most populous city. At the 2006 census, the city of Abuja had a population of 776,298, making it one of the top ten most populous cities in Nigeria. The unofficial metropolitan area of Abuja is well over three million, which would make it the fourth largest urban area in Nigeria only surpassed by Lagos, Kano and Ibadan.