Budapest is the capital and most populous city of Hungary, one of the largest cities in the European Union and sometimes described as the primate city of Hungary. It has an area of 525 square kilometres and a population of about 1.8 million within the administrative limits in 2016. It is both a city and county, and forms the centre of the Budapest Metropolitan Area, which has an area of 7,626 square kilometres and a population of 3.3 million, comprising 33 percent of the population of Hungary. Budapest became a single city occupying both banks of the Danube river with the unification of Buda and Óbuda on the west bank, with Pest on the east bank on November 17, 1873.