The Siege of Agrigentum was the first major battle between Roman and Carthaginian armies during the First Punic War. Agrigentum, a Greek city on the southern coast of Sicily, had entered into an alliance with Carthage in 264, during the campaign that had resulting in the siege of Messana. At the start of 262 the well-fortified city was the main Punic base in Sicily. The Carthaginians were reported to be recruiting a large mercenary army amongst the Celts of northern Italy, intending to assemble that army at Agrigentum. In the meantime the cities defences were in the hands of Hannibal Gisco.
The Romans responded by sending both Consuls for 262, L. Postumius and Q. Mamilius, to Sicily, at the head of an army 40,000 strong. They reached Agrigentum in the summer of 262, probably in June, and just in time to gather in the local harvest. They settled down to besiege the city. It was known that a large Punic army under the command of Hanno (one of many Hannos to be found commanding Punic forces) was being prepared to come to the aid of Hannibal, and so the Romans prepared a double line of trenches around Agrigentum.
The Carthaginian relief force took most of the rest of the year to prepare. Eventually Hanno would arrive in Sicily with a force reputed to contain 50,000 infantry, 6,000 cavalry and 60 elephants. Events around Agrigentum would suggest that this figure was fairly accurate.
The Roman siege continued uninterrupted for five months before Hanno finally arrived outside their lines. The situation inside the city was already desperate by that point, but the presence of the relief force encouraged further resistance. Hanno was able to cut the Romans off from their supplies, producing a double siege. His army must have been of sufficient size to prevent the Romans from engaging it in open battle.
The value of Rome’s alliance with Hiero II of Syracuse was now demonstrated. While the besieged garrison of Agrigentum was becoming increasingly desperate, Hiero was able to break the Carthaginian blockage of the Roman camp, running much needed supplies to his allies.
After two months outside the Roman lines, Hanno was finally forced to offer battle or see Agrigentum surrender. He was soundly defeated by the Romans, and forced to retreat west along the coast to Heraclea having lost half of his army. However, the fighting had also weakened the Romans, who were unable to prevent Hannibal from escaping from Agrigentum.
The Romans treated the captured city with unexpected severity. The city was sacked, its population, including the Greeks, sold into slavery. This had the result of turning the Greek population of Sicily against the Romans, making it much harder for them to pose as defenders of Greek liberties against Carthaginian attack. The two consuls involved in the siege of Agrigentum were not awarded a triumph, suggesting a certain dissatisfaction with their efforts.