Why it's the capital
In 1841, Prince Mihailo Obrenović moved the capital of the Principality of Serbia from Kragujevac to Belgrade. Later the city was the capital of Yugoslavia for the country's whole existence, from its creation to its break-up.
Capital of SerbiaBelgrade stands where the Sava river flows into the Danube, at the meeting point of the Pannonian Plain and the Balkan Peninsula.
In 1841, Prince Mihailo Obrenović moved the capital of the Principality of Serbia from Kragujevac to Belgrade. Later the city was the capital of Yugoslavia for the country's whole existence, from its creation to its break-up.
Follow the Danube downstream past Vienna, Bratislava and Budapest: Belgrade is the fourth and last capital city the river passes through.
Sources: Wikipedia: Belgrade, Wikipedia: Church of Saint Sava, Wikipedia: Danube