After his defeat a decade earlier in 229 BC, Demetrius of Pharos waited for an opportunity to return Illyrian piracy to the Adriatic. By 219 BC, Roman conflict with the Celts of Cisalpine Gaul, and the beginning of the 2nd Punic War against Hannibal and Carthage, encouraged Demetrius to do just that. He constructed a fleet of 90 vessels and sailed south of Lissus, violating his earlier treaty and setting off war with Rome.
The Illyrian fleet first harassed Pylos, and though initially unsuccessful, he eventually took 50 enemy ships. With this addition, he moved quickly to the Cyclades, plundering as he went.
Despite Roman occupation in other theatres, they responded hastily by sending Lucius Aemilius and a fleet across the Adriatic.
With little difficulty, the still powerful Roman navy captured Dimale, an Illyrian stronghold, and continued towards Demetrius' home base of Pharos. With diversionary tactics in the harbor, Aemilius lured the Illyrians out of their encampment while landing the main force behind Pharos. A short battle was decided in favor of the Romans, but Demetrius escaped to his allies in Macedonia.
While Rome managed to clear the Adriatic of Illyrian pirates once more, and strengthen its hold on the coastal region of Illyricum, little else could be accomplished. With Hannibal and Carthage looming as a spectre, the conquest of Illyria would not be completed until 168 BC. Even still, it would take another 40 years to organize as a province and another century again (9AD) before the whole of the Illyrian and Dalmatian tribes were under Roman control.