Located in Belgrade's municipality of Stari Grad , the fortress constitutes the specific historical core of the city. As one of the most important representatives of Belgrade's cultural heritage, it was originally protected right after World War II, among the first officially declared cultural monuments in Serbia.
Belgrade Fortress is located on top of the Belgrade Fortress is the core and the oldest section of the urban area of Belgrade. For centuries, the city population was concentrated only within the walls of the fortress, and thus the history of the fortress, until most recent times, reflects the history of Belgrade itself see: Timeline of Belgrade history. The first mention of the city is when it was founded in the 3rd century BC as " Singidunum " by the Celtic tribe of Scordisci , who had defeated Thracian and Dacian tribes that previously lived in and around the fort.
The city-fortress was later conquered by the Romans, was known as Singidunum and became a part of "the military frontier", where the Roman Empire bordered "barbarian Central Europe". Singidunum was defended by the Roman legion IV Flaviae, which built a fortified camp on a hill at the confluence of the Danube and the Sava rivers. In the period between AD and the Roman camp was repeatedly destroyed in the invasions by the Goths and the Huns.
Legend says that Attila 's grave lies at the confluence of the Sava and the Danube under the fortress. The Celtic fortification was a primitive one, located on top of Terazije ridge, above the confluence of the Sava into the Danube, where the fortress still stands today. Celts also lived in small, open and fortified settlements around the fort, called oppida. Early Singidunum reached its height with the arrival of Legio IV Flavia Felix which was transferred to the city in 86 AD and remained there until the mid 5th century.
The presence of Legio IV prompted the construction of a square-shaped castrum fort , which occupied Upper Town of today's fortress. At first, the fortress was set up as earthen bulwarks and wooden palisades, but soon after, it was fortified with stone as the first stone fort in Belgrade's history. The remains can be seen today near the northeastern corner of the acropolis.
