Illyricum was a Roman province created by Augustus in 27 BC to secure the northeastern Adriatic frontier. It combined Upper Illyricum (Dalmatia) and Lower Illyricum (Pannonia) under a governor resident at Salona, administering coastal and Danubian territories across what are now Albania, Bosnia and Herzegovina, Croatia, Hungary, Kosovo, Montenegro, Serbia, and Slovenia. The province incorporated the rugged Dinaric Alps, the eastern Adriatic islands, and the fertile Pannonian Plain, bringing Roman civil and military institutions to long-established Illyrian, Celtic, and Hellenized communities.