Pannonia, a province of the Roman empire, bounded N. and E. by the Danube, which separated it from Germany and Dacia, S. by the Save (Savus), separating it from Illyria, and W. by the Julian Alps and Mt. Cetius (now Wiener Wald), separating it from Italy and Noricum. It thus embraced the Trans-Danubian circle of Hungary, the whole of Slavonia, and parts of Croatia, Carniola, Styria, and Lower Austria. The inhabitants, mostly of Illyrian race, were divided into numerous tribes, and are described as brave and warlike, but cruel and treacherous. The Romans, by whom they were conquered under Augustus, and reconquered after a revolt and desperate struggle during the same reign, not only kept strong garrisons, but also built numerous towns and fortresses in Pannonia, among which were Vindobona (now Vienna), AEmona (Laybach), Taurunum (Semlin), Sirmium on the Save, and Mursa (Eszek). A dangerous mutiny of the Pannonian legions was quelled by Drusus shortly after the death of Augustus. The province was subsequently divided into Upper and Lower Pannonia, the former being the western, and partly separated from the latter by the Arrabo (Raab). In the reign of Gale-rius a part of Lower Pannonia was erected into a province under the name of Valeria. The three provinces subsequently formed part of the Illyrian division of the empire.

During the last period of the western empire Pannonia was successively occupied by the Huns and the Ostrogoths, and after its fall by the Longo-bards and other barbarians. The name Pannonia is frequently used for Hungary by writers of that country.