The Second Illyrian War was a short campaign in which the Romans restored the balance of power they had created at the end of the First Illyrian War, ten years earlier. The First Illyrian War had seen the Romans intervene on the east coast of the Adriatic to prevent the kingdom of the Ardiaei becoming too powerful.
The regent of the kingdom, Queen Teuta, had been deposed, but had been left with some possessions. The infant king Pinnes had remained on the Illyrian throne, although the Illyrians had been forced to renounce all claims to Corcyra, Pharos, Issa and Epidamnus. They had also agreed not to sail south of Lissus (now on the Albanian coast) with more than two unarmed ships. Finally Demetrius of Pharos, an ally of the Illyrians who had quickly changed sides when the Romans appeared, was rewarded with some possessions.
It would be Demetrius who triggered the Second Illyrian War. In the aftermath of the first war he married Triteuta, the mother of Pinnes, and became Regent of the Ardiaei. This made him the most powerful figure on the eastern shores of the Adriatic, but he was still officially a friend of Rome.
He next worried the Romans by renewing the alliance between the Illyrians and Macedonia, supplying troops to the Macedonia army that defeated the Spartans at Sellasia in 222 BC. At some point during these years he also took control of a number of cities that were seen as friends of Rome, amongst them Dimallum.
Finally, in 220 BC Demetrius allied with Scerdilaidas, another powerful Illyrian, raised a fleet of 90 light warships (lembi), and sailed south to Pylos in Messenia, far to the south of Lissus. Scerdilaidas then returned north, while Demetrius took 50 ships around the tip of Greece to raid the Cyclades islands.
Although this fleet did not attack any of Rome’s friends, the Senate saw it as a breach of the treaty. Demetrius may have been unlucky in his timing. The consuls for 219, L. Aemilius Paullus and M. Livius Salinator, had yet to hold a military command. Relations with Carthage were tense, especially in Spain, where the Second Punic War would break out in the following year, and an expedition across the Adriatic give the consuls the chance to win a triumph.
The Second Illyrian War was over very quickly. Demetrius garrisoned Dimallum and Pharos, making his own stand at Pharos. The Romans attacked Dimallum first, taking it after a seven day long siege. They then sailed along the coast to Pharos, which they captured by a stratagem. Demetrius himself escaped, and took refuge with Philip V of Macedonia where he soon established himself as one of Philip’s most important advisers, and probably played a major part in forming the alliance between Philip and Hannibal that would trigger the First Macedonian War (215-205 BC).
Curiously Scerdilaidas was not punished by Rome. Instead he became a reliable ally of the Romans, and replaced Pinnes (who is not mentioned after 217) as the main power in Illyria. For the moment the direct Roman presence on the east coast of the Adriatic ended with the fighting.