Budapest is the capital city of Hungary and the country's principal political, cultural, commercial, industrial and transportation center. Budapest has approximately 1.7 million inhabitants, down from a mid-1980s peak of 2.1 million. Budapest became a single city occupying both banks of the river Danube with the amalgamation on 17 November 1873 of right-bank Buda together with Pest on the left bank. It is the ninth largest city in the European Union.
Budapest's recorded history begins with the Roman town of Aquincum, founded around AD 89 on the site of an earlier Celtic settlement near what was to become Óbuda, and from 106 until the end of the 4th century the capital of the province of lower Pannonia. The Hungarians led by Árpád settled in the territory at the end of the 9th century, and a century later officially founded the Kingdom of Hungary. Research places the probable residence of the Árpáds an early place of central power near what became Budapest. The Tatar invasion in the 13th century quickly proved that defence is difficult on a plain. King Béla IV of Hungary therefore ordered the construction of reinforced stone walls around the towns and set his own royal palace on the top of the protecting hills of Buda. In 1361 it became the capital of Hungary.