The siege of Motyum (451 BC) was the first known attempt by the Sicel leader Ducetius to conquer an area held by one of the major Greek powers of Sicily, and led to his greatest victory over the Greeks at the battle of Motyum.
Earlier in his career Ducetius had attacked the Greek city of Catana (461 BC), but this had been in alliance with Syracuse. He had then spent the next few years securing his control over the Sicels, and by 451 BC was the leader of a powerful league. In 451 he turned on the Greeks again. His first target was Aetna, the city founded by the defeated colonists of Catana. He then turned south and besieged the city of Motyum, in the territory of Akragas. The exact location of Motyum is unknown, but one suggestion is Vassallaggi, west of Caltanissetta where the remains of a Greek settlement have been found. This would put it north-east of Akragas and west of Ducetius's main strongholds.
This direct attack on one of the main Greek powers of Sicily provoked a powerful response. Akragas and Syracuse each sent an army to try and lift the siege, but their combined force was defeated at the battle of Motyum (451 BC). Although Diodorus doesn't explicitly state that Ducetius went on to capture Motyum, the city's fortress was in his hands in the following year, so it is safe to assume that the garrison surrendered after the failure of the relief army.