Octavian celebrates the first of three consecutive triumphs at Rome, this one celebrated his victory over Illyricum. The war against Illyricum actually took place several years earlier.
Octavian’s campaigns in Illyria lasted only two years from 35 – 33 BC. At the head of ten legions, he marched from the north and subjugated the Iapydes, the Liburnians and the Delmatae. Octavian led the campaign against the Iapydes himself assigning the other tribes to subordinate commanders. The Cisalpine Iapydes (on the Adriatic side of the mountain range) did not pose a significant problem to Octavian however those on the other side (the transalpine Iapydes) were much more difficult to defeat.
These campaigns represent the first concerted effort to establish lasting control in the region. The level of success achieved by Octavian is still a matter of significant debate in particular the extent of his conquest remains far from clear with some authors suggesting that he conquered all of Illyricum and others suggesting only a small tract of Dalmatia and Pannonia were subjugated.