The Second Battle of Capua was fought in 211 BC, when the Romans besieged Capua. It is described by Polybius at 9.4-7, and by Livy at 26.4-6.
Capua had defected to Hannibal after the Battle of Cannae in 216 BC. Hannibal had made Capua his winter quarter in 215 BC and had conducted his campaigns against Nola and Casilinum from there. The Romans had attempted to march on Capua several times since its defection but were thwarted by the return of Hannibal's army rushing to its defence; the latest attempt had cost them some 18,000 men at the Battle of Herdonia in 212 BC. By 211 BC, Hannibal was busy in the south of Italia and the Romans were ready to try again, banking on taking it before Hannibal's army could return to Capua.
Hannibal feared that if he approached Capua, the Romans would simply withdraw, as they had done on other occasions, only to return to lay siege again once he had left. He thus tried to break the siege by marching on Rome itself, hoping that that threat would force the Roman army to break off the siege and march back to Rome to defend it. Once the Roman army was in the open, he would then turn to engage it in a pitched battle and defeat them once again, freeing Capua from the threat. However, Hannibal found the defences of Rome too formidable for an assault and as he had only planned this movement as a feint, he lacked both the supplies and equipment for a siege. The Roman besiegers of Capua, knowing this, ignored his march on Rome and refused to break off their siege. His feint having failed, Hannibal was forced to retreat south and Capua unrelieved fell to the Romans shortly afterwards.