Pannonia , Province of the Roman Empire, corresponds to today's West Hungary and split East Austria as well as parts of several Balkan states, especially Slovenia , Croatia and Serbia (Vojvodina). The Pannonians were mainly Illyrians, but there were some Celts in the western part of the province.
The Roman conquest of the area began in 35 bce under Octavian (who later became the emperor Augustus) and was completed in 14 bce with the capture of Sirmium (Sremska Mitrovica, Vojvodina), the key town of the Sava River valley. The Pannonian tribes, joined by the Dalmatians, revolted in 6 ce, posing the gravest threat to Italy since Hannibal's invasion. After the revolt was put down, Pannonia was organized as a separate province in 9 ce and garrisoned with three legions.
The Emperor Trajan divided the province by 106 ce . The western and northern districts formed Pannonia Superior, which was the focus of the Roman wars with the Markomann in the dominion of Marcus Aurelius (reigned 161-180), who died at Vindobona (Vienna). The southern and eastern districts have been Diocletian (284–305) organized as Pannonia Inferior . Pannonia Superior has been subdivided into Pannonia Prima and Pannonia Ripariensis (or Savia), and Pannonia Inferior has been subdivided into Valeria and Pannonia Secunda.
The inhabitants of Pannonia retained their own culture into the 2nd century ce, but Romanization did proceed rapidly, especially in the west. In the 1st century ce Emona (Ljubljana, Slovenia) and Savaria (Szombathely, Hungary) were made Roman colonies, and Scarbantia (Sopron, Hungary) and other cities were made municipia (self-governing communities). Pannonia was the birthplace of several Roman emperors of the 3rd century, and the province provided large numbers of troops for the Roman army. The grave barbarian threat in the 4th century ce forced the Romans to withdraw after 395. From that time Pannonia ceased to exist as a separate unit.