As Rome and Carthage occupied each other in Sicily, Africa and throughout the Mediterranean, Rome's northern neighbors began to gather strength and cause problems of their own. In Illyria, King Agron, between the years 233 and 231 BC, had gathered a formidable fleet and started to sanction naval operations against various Greek city states. In 231, Illyrian success was so great against the Aetolians, Polybius tells us, that he "made so merry that he caught a cough and died."
Agron was succeeded by his wife, Queen Teuta. The taste of success left by her husband encouraged her to sanction increased piracy in the Adriatic and Ionium seas. Towns up and down the Epirus and Achaea coasts were plundered, harassed and virtually under siege by sea. Rome, having gained regional authority with its earlier victories over Pyrrhus and Carthage and having built a powerful fleet as a result, was pleaded to by Greek merchants to quell the pirates. By 230 BC, even Italian and Roman trade routes were beginning to suffer and Rome had no choice but to intervene.
The Senate, again according to Polybius, sent Gaius and Lucius Coruncanius, to treat with Queen Teuta. She, as many of the early Roman conquest stories go, met the Roman envoys with indignation. The queen would only guarantee that her official forces would refrain from attacking Roman interests, but that she was not responsible for the actions of pirates. After a heated exchange, the Romans left to return without a satisfactory agreement, but Teuta still angry over the argument with the Romans, had one of the envoys killed en route.
Once again, Rome used a real or perhaps fabricated injustice as cause for war and expansion. With Macedonia, Illyricum's main regional ally, occupied in its own expansionist endeavors, and Carthage in the midst of quelling its own mercenary revolt, the timing was right to move north. In 229 BC, Consul Gnaeus Fulvius sailed for Illyria with a fleet of 200 quinqueremes, while his Co-Consul Aulus Postumius took legions by land. Fulvius initially attempted to relieve a siege of Corcyra by the Illyrians under the command of Demetrius of Pharos, but he was too late to prevent its success. However, recognizing the authority of the Roman military, Demetrius quickly handed the island over to Roman protection.
The fleet joined the Legions at Apollonia and moved north into Illyrian territory. It cleared pirate vessels as it went, while the pressure of the army forced Teuta and Demetrius to abandon the sieges of Dyrrhachium and Issa. Both cities fell under the 'protection' of Rome as well as several smaller towns along the coast. Teuta meanwhile, had little choice but to give up her aggressive tactics and withdraw to her winter quarters.
In the spring of 228 BC, Illyricum sued for peace and received harsh terms. Teuta was forced to cede portions of her kingdom along the coast (120 miles) to Roman control, along with an unspecified tribute. Of more important concern to the issue of piracy, Illyrian fleets were no longer allowed to sail south of Lissus with more than two ships. Demetrius also accepted Roman terms and established Pharos as a client kingdom forming a natural buffer with Macedonia.
The result of the Illyrian War, while minor in comparison to other conflicts, had a direct impact on future relations with Macedonia and Carthage. Removing the Illyrian piracy threat from the Adriatic greatly improved Roman relations with the Greeks of Corcyra, Epidamnus and Appollonia as well as the whole state of Achaea. Macedonia, previously the superior power of the Greek world, was angered by Roman interference in what it considered to be its own affair. That anger would boil over into the second Punic War and develop into an alliance with Carthage adding to Rome's concerns over the next century.