Belgrade Fortress (Serbian: Београдска тврђава), represent old citadel (Upper and Lower Town) and Kalemegdan Park (Large and Little Kalemegdan) on the confluence of the River Sava and Danube, in an urban area of modern Belgrade, the capital of Serbia. It is located in Belgrade’s municipality of Stari Grad. Belgrade Fortress was declared Monument of Culture of Exceptional Importance in 1979, and it is protected by Republic of Serbia. Belgrade Fortress is the core and the oldest section of the urban area of Belgrade and for centuries the city population was concentrated only within the walls of the fortress, thus the history of the fortress, until most recent history, equals the history of Belgrade itself. First mention of the city is when it was founded in the 3rd century BC as “Singidunum” by the Celtic tribe of Scordisci. The city-fortress was later conquered by the Romans, became known as Singidunum and became a part of “the military frontier”, where the Roman Empire bordered “barbaric Central Europe”. The Byzantine Emperor Justinian I rebuilt the Fortress around 535. In the following centuries a fortress suffered continuous destruction under the Avar sieges. The name Belgrade (or Београд, in Serbian), which, not just in Serbian but in most Slavic languages means a “white town” or a “white fortress”, was first mentioned in AD 878 in Papal letter. The Fortress kept changing its masters: Bulgaria, Byzantines Serbs, and Hugarians. Fortress was rebuilt few times, by Bela I of Hungary, by Byzantine, Emperor Manuel I, by Serbian Despot Stefan Lazrević. In 1521. it fell in Turkish hands. During the period of short Austrian rule (1718–1738) the fortress was largely rebuilt and modernized. It witnessed two Serbian Uprisings in the 19th century, the Great Serbian Migration in the 17th century, the Turkish Period. The fortress suffered further damages during the First and the Second world wars. After almost two millennia of continuous sieges, battles and conquests the fortress is today known as the Belgrade Fortress.