Syrmia is a fertile region of the Pannonian Plain in Europe, which lies between the Danube and Sava rivers. The majority of Syrmia is placed within the Srem and South Backa districts of the Autonomous Province of Vojvodina in Serbia. A smaller area around Novi Beograd, Zemun, and Surcin belongs to the City of Belgrade. The final part of Syrmia is divided between multiple municipalities in Serbia and Vukovar-Srijem County in Croatia.
Sirmium become conquered by using Romans in the first century BC and became the financial and political capital of Pannonia. In 6 AD, there has been an uprising of the indigenous peoples in opposition to Roman rule. However, ten later Roman Emperors have been born in Sirmium or close by. They covered Herennius Etruscus, Hostilian, Decius Traian, Claudius II, Quintillus, Aurelian, Probus, Maximianus Herculius, Constantius II and Gratian.
These emperors had been usually Romanised Illyrians. In the 6th century AD, Pannonia, turned into a province of the Byzantine Empire. Through vassal arrangements, Sermia fell beneath manipulate of various rulers. In the 7th century AD, the ruler of Syrmia became Kuber, a Bulgar leader, who changed into a vassal of the Avars. In the early ninth century AD, Syrmia was a part of the Slavic kingdom of Pannonian Croatia. The ruler, Prince Ljudevit Posavski lost manage to the Franks. In 827 AD the Bulgars again and endured to rule after a peace treaty in 845 AD.