Sremska Mitrovica is one of the oldest cities in Europe. Archaeologists have found a trace of organized human life dating from the 5000 BC onwards. Ionian jewellery dating to 500BC was excavated in the city. When the Romans conquered the city in the 1st century BC, Sirmium already was a settlement with a long tradition.
In the 1st century, Sirmium gained a status of a colony of the citizens of Rome, and became a very important military and strategic location in Pannonia province. The war expeditions of Roman emperors Traian, Marcus Aurelius, and Claudius II, were prepared in Sirmium.
In 103, Pannonia was split into two provinces: Upper Pannonia and Lower Pannonia, and Sirmium became the capital city of Lower Pannonia. In 296, Diocletian operated a new territorial division of Pannonia. Instead of previous two provinces, there were four new provinces established in former territory of original Pannonia: Pannonia Prima, Pannonia Valeria, Pannonia Savia and Pannonia Secunda. Capital city of Pannonia Secunda was Sirmium.
In 293, with the establishment of tetrarchy, the Roman Empire was split into four parts; Sirmium became one of the four capital cities of Roman Empire, the other three being Augusta Treverorum, Mediolanum, and Nicomedia (modern Trier, Milan and Izmit). During the tetrarchy, Sirmium was the capital of emperor Galerius. With the establishment of praetorian prefectures in 318, the capital of the prefecture of Illyricum was Sirmium.
Since the 4th century, the city was an important Christian centre, and was a seat of the Episcopate of Sirmium. Four Christian councils were held in Sirmium.
At the end of the 4th century, Sirmium was brought under the sway of the Goths, and later, was again annexed to the Eastern Roman Empire. In 441, Sirmium was conquered by the Huns, and after this conquest, it remained for more than a century in the hands of various Barbarian tribes, such were Eastern Goths and Gepids. For a short time, Sirmium was the center of the Gepide State and the king Cunimund minted golden coins in it. After 567, Sirmium was again included into Eastern Roman Empire. The city was finally conquered and destroyed by Avars in 582. This event marked the end of the period of late Antiquity in the history of Sirmium.
11 luxurious golden belts of Avar handicraft dating to the 6th century was excavated in the vicinity.