The Danube is the longest river in the European Union and Europe's second longest river after the Volga. Szechenyi Chain Bridge spans the Danube River at Budapest, Hungary. It was the first permanent bridge across the Danube, built in 1849. Budapest is the capital and largest city of Hungary. It became a single city in 1873 with incorporation of Buda (west bank) and Pest (east bank). It was the second capital of the Austrian-Hungarian Empire. It is regarded as one of the most beautiful cities in Europe, and is a UN World Heritage Site.