The siege of Corfinium (early 49 BC) was the first military action of the Great Roman Civil War and saw Caesar quickly overwhelm an attempt to defend the city against him.
At the start of the war Caesar only had one legion, the 13th, with him in northern Italy. In theory the Senate’s forces, commanded by Pompey, outnumbered Caesar’s force, but they were caught out by Caesar’s rapid advance into central Italy. Pompey quickly decided that he couldn’t hold Rome, and decided with withdraw from the city. He moved south-east into Apulia, from where he planned to escape to Greece with his army and as much of the Senate as possible.
L. Domitius Ahenobarbus, officially Caesar’s replacement as proconsul of Transalpine Gaul, decided to ignore Pompey’s orders. He had managed to gather twenty cohorts from Alba, the Marsi, Peligni and nearby provinces, and had been joined by another thirteen cohorts that had been raised by Lucilius Hirus. In theory he thus outnumbered Caesar, who now had two legions, having been joined by the 12th Legion. Ahenobarbus decided to defend Corfinium, on the eastern side of the Appenines, east of Rome, and a key position if Caesar decided to try and catch Pompey.
Caesar captured Asculum and then advanced rapidly towards Corfinium. As he was approaching the city he ran into five cohorts from the garrison who had been sent out to destroy a bridge three miles outside the walls. Caesar’s advanced guard clashed with these troops and forced them to retreat back to Corfinium. Caesar then followed up with his main force and camped under the walls.
We have two main accounts of the resulting siege, one from Appian and one from Caesar himself. Appian’s account is fairly short. Caesar besieged the town. Ahenobarbus attempted to escape, but was captured by the inhabitants of the town who handed him over to Caesar. Caesar demonstrated his famous clemency, accepted Ahenobarbus’s men into his own ranks, and allowing Ahenobarbus to go wherever he wanted, taking his money with him.
Caesar provides a longer account. Ahenobarbus made a determined attempt to hold the town. He sent messages to Pompey asking him to bring up his army and trap Caesar against the walls. He placed siege engines around the walls, took personal command of the deployment of his troops, and even promised each of the defenders four acres of land from his private estates.
In the meantime Caesar’s army was expanding. Part of the 7th legion arrived, after taking Sulmona. The 8th Legion arrived with 22 cohorts from Gaul, and he used them to form a second camp. For three days Caesar concentrated on strengthening his camp and building defensive works to surround the town.
Just before this work was complete, a message arrived from Pompey. He refused to risk his armies to defend Ahenobarbus, who had decided to shut himself up in Corfinium without any orders. Pompey ordered him to extract himself from the trap using his own efforts, and join Pompey’s main army. However by the time this message arrived Caesar’s lines were almost complete and it was no longer possible for Ahenobarbus’s men to escape. He himself began to prepare to escape from the city.
Ahenobarbus attempted to keep the news from Pompey from his men, but it soon leaked to them. His men began to meet in the evening, and many of them declared that he was time for them to look to their own safety. At first the Marsi resisted this, and the garrison was almost split by a civil war of its own. The issue was decided when the troops learnt that Ahenobarbus was planning to flee. At that point they captured their commander, and offered to surrender him to Caesar.
Caesar accepted their surrender on the following morning. He set free all of the senators, knights and local nobles who had been in the city, and even returned six million sesterces to Ahenobarbus, in an attempt to win them over to his cause. He then accepted the allegiance of Ahenobarbus’s men, greatly strengthening his army. Caesar spent seven days at Corfinium in total, and then moved south to Apulia, where he attempted to catch Pompey at Brundusium.