Buda is the part of Budapest, the capital city of Hungary, that lies on the western bank of the Danube. Historically, "Buda" referred only to the royal walled city on Castle Hill, which was constructed by Béla IV between 1247 and 1249 and subsequently served as the capital of the Kingdom of Hungary from 1361 to 1873. In 1873, Buda was administratively unified with Pest and Óbuda to form modern Budapest.