In the aftermath of their victory in the battle of Panormus (251 B.C.), the Roman Senate decided to make a determined effort to end the fighting on Sicily (First Punic War). Accordingly, they raised a new fleet, containing 240 ships. The two consuls for 250 were both sent to Sicily, with four legions. The combined Roman force could have contained as many as 100,000 men, including the crews of the warships and the auxiliary troops that normally accompanied the legions.
At first the Romans conducted a vigorous siege. The consuls of 250, C. Atilius Regulus and Manlius Vulso Longus, were both experience men who had served as consuls before. They built siege works around the city, constructed battering rams, catapults and siege towers, attempted to mine under the city walls and to block the harbour.
At this early point in the siege, the defence relied almost entirely on a force of 10,000 mercenaries within the city. According to Polybius the Carthaginians came close to disaster when some of the mercenary commanders inside Lilybaeum decided to defect to the Romans. Luckily the plot was detected, and the guilty parties found themselves unable to return to the city from the Roman camp. The mercenaries themselves remained loyal, and soon after this an equally large force of reinforcements reached the city from Africa. The fleet that had brought those reinforcements then sailed to the nearby Carthaginian base at Drepana, from where they able to provide valuable support to the besieged garrison.
Two events prevented the Romans from continuing to conduct such a vigorous siege. First, a destructive gale blew up around Lilybaeum, sweeping away many of the protective structures surround the Roman siege engines. Taking advantage of this the defenders of the city set fire to the vulnerable siege engines, and fanned by the winds fire destroyed the majority of the Roman siege engines.
This damage could have been repaired given time, but for the next blow to befall the Romans. With the new year came new consuls, and reinforcements for the fleet. The senior consul, Publius Claudius Pulcher, decided to launch a surprise attack on the Carthaginian fleet at Drepanum. The resulting battle of Drepanum was the only serious Roman naval defeat of the war. Ninety three of their ships were captured by the Carthaginians, and perhaps only 30 escaped. Claudius was disgraced, recalled to Rome, and fined. Soon after the defeat at Drepanum a supply fleet under the second consul, L. Junius Pullus, was destroyed by a combination of Carthaginian action and bad weather. Without a fleet, the Romans could not properly blockade Lilybaeum, and so were forced to settle down for a long siege.
The defeat at Drepanum seems to have ended the active phase of the siege of Lilybaeum. The Romans arranged for supplies to be carted across the length of Sicily, and made some attempts to isolate Drepanum. Carthage appointed Hamilcar Barca to command on Sicily in 247 B.C., and he concentrated his efforts elsewhere on the island. The siege of Lilybaeum only ended after the Romans had won a decisive naval victory at the battle of the Aegates Islands (241 B.C.). This defeat finally forced Carthage to negotiate for peace on Roman terms. One of the terms of the peace treaty saw Carthage evacuate its last possessions on Sicily, amongst them Lilybaeum.