The Battle of Mutina took place on 21 April 43 BC between the forces loyal to the Senate under Consuls Gaius Vibius Pansa and Aulus Hirtius, supported by the forces of Caesar Octavian, and the forces of Mark Antony which were besieging the troops of Decimus Brutus. The latter, one of Caesar's assassins, held the city of Mutina (present-day Modena) in Cisalpine Gaul.
Six days earlier, the Battle of Forum Gallorum had ended with heavy losses on both sides and the mortal wounding of consul Pansa. Hirtius and Octavian then launched an attack on Antony's camp, seeking to break the siege. Amid bloody fighting, Hirtius was killed, leaving the army and republic leaderless. Octavian saw action in the battle, recovered Hirtius' body, and managed to avoid defeat. Decimus Brutus also participated in the fighting with part of his forces locked up in the city. Command of Hirtius' legions then devolved to Caesar Octavian. Decimus Brutus, marginalized after the battle, soon fled Italy in the hopes of joining fellow assassins Marcus Junius Brutus and Gaius Cassius Longinus; he was, however, captured and executed en route.
After the battle, Mark Antony decided to give up the siege and retreated westward along the via Aemilia, escaping the enemy forces and rejoining the reinforcements of his lieutenant Publius Ventidius Bassus. The battle brought the brief War of Mutina to a victorious end for the Republicans allied with Caesar Octavian, but the situation would change completely the following autumn with the formation of the Second Triumvirate of Antony, Octavian, and Lepidus.
Background
At the start of the War of Mutina in December 44 BC, Mark Antony besieged Decimus Junius Brutus Albinus – the governor of Cisalpine Gaul – in Mutina in an attempt to force him to surrender the province to him in accordance with an illegal law he had passed earlier that year in June. Over some months, relations between Antony and the Senate in Rome broke down. The consuls for 43 BC – Aulus Hirtius and Gaius Vibius Pansa – were then dispatched north to relieve Decimus Brutus. Joining them was the private army of Caesar's adoptive heir, Octavian, whose command had been legitimised by the Senate.
As Pansa's army moved to join Hirtius, who had previously moved north, Antony ambushed it on the Via Aemilia at the Battle of Forum Gallorum. Successful in defeating and mortally wounding Pansa, his forces were however then themselves set upon by Hirtius and Octavian's veteran forces and were forced to retreat back to the siege works at Mutina. Hirtius and Octavian then moved to engage Antony's forces and relieve the city.
Battle
Attack on the camps of Mark Antony
Initial news in Rome claimed that the Senate's forces had suffered a defeat at Forum Gallorum, arousing concern and fears among the Republican faction. Only on 18 April did they receive Aulus Hirtius' letter and a report detailing the events of the battle. The victory at Forum Gallorum, wrongly considered decisive, was greeted with enthusiasm; Antony was roundly denounced and his sympathizers forced into hiding. In the Senate on 21 April 43 BC, Cicero emphatically pronounced the Fourteenth and final Philippic, in which he exulted in the victory at Forum Gallorum, proposed forty days of public thanksgiving, and particularly praised the legionaries who had fallen and the two consuls Aulus Hirtius and Vibius Pansa. The latter was injured, but his life did not then seem in danger. The orator rather minimized the contribution of Caesar Octavian, although the young man, despite his minor role in the battle, had been acclaimed imperator on the field by the troops, as had the two consuls Hirtius and Pansa.