Piso was forgiven in a general amnesty and seemed to come to terms with Caesar's victory. But when the dictator's assassination in 44 sparked the War of the Second Triumvirate he aligned himself with the assassins of Caesar, the "Liberatores", joining the armies of Gaius Cassius Longinus (Cassius) and Marcus Junius Brutus the Younger (Brutus). They were defeated at the hard-fought Battle of Philippi in 42, which involved 200,000 soldiers. Piso commanded troops during the campaign, but his precise role is not known. He was again pardoned and returned to Rome, where he refused to participate in the political arena which was under the control of Caesar's heir, Caesar Octavianus (the future Augustus).