*The Romans cross the Adriatic: 229 B. C.* In the next spring, 229 B. C., the Romans sent against the Illyrians a fleet and an army of such strength that the latter could offer but little resistance and in the next year were forced to sue for peace. Teuta had to give up a large part of her territory, to bind herself not to send a fleet into the Ionian sea, and to pay tribute to Rome. Corcyra, Epidamnus, Apollonia, and other cities became Roman allies.
The fact that Rome first crossed the Adriatic to prosecute a war against the Illyrians placed her in hostility to their ally, Macedonia, the greatest of the Greek states. And although Macedonia had been unable to offer aid to the Illyrians because of dynastic troubles that had followed the death of King Demetrius (229 B. C.), the Macedonians regarded with jealous suspicion Rome's success and the establishment of a Roman sphere of influence east of the Adriatic. Conversely, the war had established friendly relations and coöperation between Rome and the foes of Macedon, the Aetolian and Achaean Confederacies, which rejoiced in the accession of such a powerful friend. The way was thus paved for the participation of Rome, as a partizan of the anti-Macedonian faction, in the struggles which had so long divided the Greek world.
*The second Illyrian war: 220-219 B. C.* The revival of Macedonian influence led indirectly to Rome's second Illyrian war. The alliance of Antigonus Doson with the Achaean Confederacy and his conquest of Sparta (222 B. C.) united almost the whole of Greece under Macedonian suzerainty. Thereupon Demetrius of Pharos, a despot whose rule Rome had established in Corcyra, went over to Macedonia, attacked the cities allied with Rome, and sent a piratical squadron into Greek waters (220 B. C.). Rome, now threatened with a second Carthaginian War, acted with energy. Macedonia, under Philip V, the successor of Antigonus Doson, was involved in a war with the Aetolians and their allies. Deprived of support from this quarter Demetrius was speedily driven to take refuge in flight. His subjects surrendered and Rome took possession of his chief fortresses, Pharos and Dimillos.
*War with the Gauls in North Italy: 225-22 B. C.* In the interval between these Illyrian Wars Rome became involved in a serious conflict with the Gallic tribes settled in the Po valley. For about half a century this people had lived at peace with Rome, ceasing their raids into the peninsula and becoming a prosperous agricultural and pastoral people. It is claimed that they became alarmed at the Roman assignment of the public land on their southern borders, called the Ager Gallicus, to individual colonists in 233 B. C., and that this caused them to take up arms. However, this territory had been Roman since 283 B. C. and its settlement could hardly have been interpreted as an hostile act. More probable is it that the cause of the new Gallic invasion was the coming of fresh swarms from across the Alps, which some of the Cisalpine Gauls, who had forgotten the defeats of the previous generation, perhaps invited, and certainly joined, for the sake of plunder. In 238 such a band of Transalpines crossed the Roman frontier and penetrated as far as Ariminum, but serious dissensions broke out within their own ranks and they had to withdraw. There was no further inroad attempted until 225 B. C.