The territory of today’s Belgrade was inhabited, as the records show, early as the 3rd century BC. Objects that have been preserved from these historical periods can be seen on the Kalemegdan Fortress during your Belgrade Tour. Not many objects were left to testify about these ancient times because the city of Belgrade was demolished to the ground many times in its history, some historians refer to it as the “Gates of War”.
Singidunum is the name for the ancient city on the location of the today’s Belgrade, the capital of Serbia. It was recorded that a Celtic tribe, the Scordisci, settled the area in the 3rd century BC following the Gallic invasion of the Balkans. The Roman Empire conquered the area in 75 BC and later garrisoned the Roman Legio IV Flavia Felix there in 86 AD. It was the birthplace to the Roman Emperor Jovian. Belgrade has arisen from its ashes 38 times.
The Gallic invasion of the Balkans brought the settlement of the Scordisci who picked the strategic hilltop at the meeting of the two rivers as the basis for their habitation. The name Singidun is first attested in 279 BC The name has Celtic dūn(on) "enclosure, fortress" as its second element. For singi- there are several theories, the two most widely circulated being that it is a Celtic word for circle, hence "round fort", or it could be named after the Sings, a Thracian tribe that occupied the area prior to the arrival of the Scordisci. There is only limited archeological evidence of the city's foundational period, including some burial sites with grave goods.
The archeological site of the Ancient Singidunum comprises of the castrum, civil dwellings and necropolises. In the first centuries AC the Singidunum was an important strategic fortification on the borderline to barbaric lands. In the first century AC the Fourth Flavia was stationed on the site where the large Castrum was built to serve its needs, which is situated today on the upper part plateau of the Belgrade Fortress. The specific of the geographic location on the crossroads of the military and trade routes had influenced the development of an economically strong civil settlement which went through all the stages of the Roman provincial towns. The necropolis surrounded the civil settlement.
Singidunum reached its height with the arrival of Legio IV Flavia Felix in 86 AD. The legion set up as a square-shaped Castrum (fort), which occupied Upper Town of today's Kalemegdan. At first, the fortress was set up as earthen bulwarks, but soon after, it was fortified with stone, the remains of which can be seen today near the northeastern corner of the acropolis.
In time, a large settlement grew out from around the Castrum. The town took on a rectilinear construction, with its streets meeting at right angles. The grid structure can be seen in today's Belgrade with the orientation of the streets Uzun Mirkova, Dušanova, and Kralja Petra I. Studentski Trg (Students' Square) was a Roman forum, bordered by thermae (a public bath complex whose remains were discovered during the 1970s) and also preserves the orientation the Romans gave Singidunum. Other remnants of Roman material culture such as tombs, monuments, sculptures, ceramics, and coins have been found villages and towns surrounding Belgrade.
Systematic digging and accidental findings had revealed many archeological objects, remnants of profane, religious and funerary architecture, sculptures, numerous epigraphic remains, ceramics and other movable material.
The Slavic Beograd, the "white city" (named for the color of the stone it was built from), had been established by the 9th century on the site of Singidunum, within the First Bulgarian Empire. It is first mentioned in a letter written on 16 April 878 by Pope John VIII to Bulgarian prince Boris I Mihail. With its new name, Belgrade would eventually be restored to its earlier strategic significance.