Budapest is the capital and most populous city of Hungary. It is the ninth-largest city in the European Union by population within city limits; the city has an estimated population of 1,752,286 over a land area of about 525 square kilometres. Budapest, which is both a city and county, forms the centre of the Budapest metropolitan area, which has an area of 7,626 square kilometres and a population of 3,303,786, comprising 33% of the population of Hungary.
The history of Budapest began when an early Celtic settlement transformed into the Roman town of Aquincum, the capital of Lower Pannonia. The Hungarians arrived in the territory in the late 9th century, but the area was pillaged by the Mongols in 1241–42. Re-established Buda became one of the centres of Renaissance humanist culture by the 15th century. The Battle of Mohács, in 1526, was followed by nearly 150 years of Ottoman rule. After the reconquest of Buda in 1686, the region entered a new age of prosperity, with Pest-Buda becoming a global city after the unification of Buda, Óbuda and Pest on 17 November 1873, with the name 'Budapest' given to the new capital.