Abuja is the capital city of Nigeria located in the centre of the country within the Federal Capital Territory (FCT). It is a planned city and was built mainly in the 1980s, replacing the country's most populous city of Lagos as the capital on 12 December 1991. Abuja's geography is defined by Aso Rock, a 400-metre (1,300 ft) monolith left by water erosion. The Presidential Complex, National Assembly, Supreme Court and much of the city extend to the south of the rock. Zuma Rock, a 792-metre (2,598 ft) monolith, lies just north of the city on the road to Kaduna State.
At the 2006 census, the city of Abuja had a population of 776,298, making it one of the ten most populous cities in Nigeria. According to the United Nations, Abuja grew by 139.7% between 2000 and 2010, making it the fastest growing city in the world. As of 2015, the city is still experiencing an annual growth of at least 35%, still retaining its position as the fastest-growing city on the African continent and one of the fastest-growing in the world. Abuja has witnessed a huge influx of people into the city; the growth has led to the emergence of satellite towns, such as Karu Urban Area, Suleja, Gwagwalada, Lugbe, Kuje and smaller settlements towards which the planned city is sprawling. The unofficial metropolitan area of Abuja has a population of well over three million, making it the fourth largest metropolitan area in Nigeria, surpassed only by Lagos, Kano and Ibadan. As at 2016, the metropolitan area of Abuja is estimated at 6 million persons, placing it behind only Lagos, as the most populous metro area.
Major religious sites include the Nigerian National Mosque and the Nigerian National Christian Centre. The city is served by the Nnamdi Azikiwe International Airport. Abuja is known for being one of the few purpose-built capital cities in Africa, as well as being one of the wealthiest.