The winter of 264/263 had been spend with a discussion about an appeal for help from the Mamertines, a group of pirates that lived in Messana and controlled the strait between Italy and Sicily. They had been under attack from Hiero II, the tyrant (later king) of Syracuse, and some Mamertines had asked help from Carthage, others in Rome. The Carthaginian admiral Hannibal, who happened to be on the nearby Aeolian Islands, was the first to offer assistance, and had garrisoned Messana.
Was Rome to help the Mamertines? The issue was complex. As pirates, they did not deserve it; but Carthage could not be allowed to control the strait either. Besides, if Rome did not do anything, Carthage's next step would be the conquest of Syracuse, and then it would control all of Sicily, which was unacceptable. The Senate was divided, but the People's Assembly was for offering help to the Mamertines, even if this meant a crisis that could lead to war with Carthage.
Therefore, consul Appius Claudius Caudex was ordered to cross to Sicily with two legions. He occupied Rhegium, on the other side of the strait, and under cover of the night, a military tribune named Gaius Claudius crossed to Messana. He announced that he would liberate the people, received an enthusiastic reply, and tried to return with a greater fleet, but unaware of the currents and outsmarted by the Carthaginians, he lost some ships. The liberation of Messana had to be postponed.
The Carthaginian commander of Messana, a man named Hanno, sent back the captured ships and men, hoping that the Romans would understand that it was useless to invade Sicily, and hoping that this gesture might prevent full-scale war. It did not work. Gaius Claudius crossed the strait for the third time, and because he now understood the currents, was able to capture the harbor before the Carthaginians understood what was going on. Hanno took refuge in the citadel, and was given a safe-conduct. The Carthaginian authorities would later order his crucifixion.
Now, the Romans were in Messana, and Hiero II of Syracuse and the Carthaginians decided that they should conclude an alliance against Rome. The two states had been archenemies for more than two centuries, and the Romans can not have expected this remarkable diplomatic initiative. Yet, the two allies wanted to keep Rome out of Sicily, and may have thought that after this had been achieved, they could still resume their eternal war and fight for Messana. Hiero and Hanno marched on Messana: the first built his camp to the south, the second in the west, and the Carthaginian navy occupied a place in the north.
Until this moment, war could have been prevented. The local commander of Messana had preferred to retreat, accepting defeat as the price of peace. Now, Appius Claudius Caudex, as chief magistrate of Rome, sent an envoy to the besiegers, demanding that they would go away. When they refused, he declared war.
In an intentionally simple line, the poet Ennius, one of the oldest sources for this conflict, describes what happened: Appius indixit Karthaginiensibus bellum ("Appius proclaimed war against the Carthaginians"). His generation knew that the First Punic War had been the greatest war ever, and had seen the almost equally dramatic Second Punic War. Any reader would have appreciated the contrast between the significance of the event and the simplicity of Ennius' remark.
Appius Claudius Caudex acted quickly. He immediately attacked Hiero, and proceeded to the camp of Hanno. The Greek and the Carthaginian both claimed that they had won the encounter, but the simple fact is that Hiero returned to Syracuse and opened negotiations; and that Hanno went to Acragas and sent garrisons to several towns. Even if Rome had lost the double battle, Claudius had achieved a diplomatic victory: in the following year, Syracuse switched sides.
The successful crossing to Sicily was the first Roman victory in a war that was to last for another twenty-two years, and this First Punic War was, as the Greek historian Polybius of Megalopolis was to write later, "the longest and most severely contested war in history".note[Polybius, World History 1.63.4-5.]