The Battle of Forum Gallorum was fought on 14 April 43 BC between the forces of Mark Antony and legions loyal to the Roman Senate under the overall command of consul Gaius Pansa, aided by his fellow consul Aulus Hirtius. The untested Caesar Octavian (the future emperor Augustus) guarded the Senate's camp. The battle occurred on the Via Aemilia near a village in northern Italy, perhaps near modern-day Castelfranco Emilia.
Antony was attempting to capture the province of Cisalpine Gaul from its appointed governor, Decimus Brutus. Brutus was besieged by Antony in Mutina (modern Modena), just south of the Padus (Po) River on the Via Aemilia. The Roman Senate sent all its available forces to confront Antony and relieve Brutus. Hirtius and Octavian arrived near Mutina with five veteran legions, where they waited for Pansa, who was marching north from Rome with a further four legions of recruits. Antony had four veteran legions in addition to the troops that were besieging Mutina. Aware that he would soon be outnumbered, Antony sought to defeat his opponents in detail before they could link up. After failing to provoke a battle with Hirtius, Antony marched two of his legions between the two Senatorial armies and laid an ambush on Pansa's approaching recruits. Unknown to Antony, Pansa had already been joined by one of Hirtius' veteran legions and Octavian's praetorian cohorts.
Antony's forces caught Pansa's army by surprise on a narrow road surrounded by marshes. A bitter, bloody battle ensued, in which Antony's II and XXXV legions defeated Pansa's troops and forced them to retreat southwards. Pansa himself was severely wounded. Antony called off the pursuit of Pansa's broken army and began marching his jubilant troops back towards Mutina. Hirtius then arrived from the north with a single veteran legion, which crashed into Anthony's exhausted troops, taking two Roman eagles and 60 standards. Antony's victory was turned into a major defeat; he fell back with his cavalry to his camp outside Mutina.
After receiving a report of the battle, Marcus Tullius Cicero, a fierce adversary of the Antonian faction, pronounced in the Senate the Fourteenth Philippic, exalting the success and praising the two consuls and young Caesar Octavian. Nevertheless, the battle was not decisive and the campaign continued. The two armies fought again seven days later (21 April) at the Battle of Mutina, which forced Antony to abandon the siege of the city and retreat westward. Hirtius was killed in the fighting at Mutina; Pansa was still recovering from his wound at Forum Gallorum but died on 23 April in unexplained circumstances.
Background
After the assassination of Julius Caesar, Antony's relations with Caesar's adoptive heir Octavian and the rest of the Roman Senate broke down. At the start of the War of Mutina in late 44 BC, he moved to invest the homonymous city in an attempt to force Decimus Junius Brutus Albinus, the governor of Cisalpine Gaul, to give it up to him in accordance with an illegal law he had passed the previously that year in June.
At the start of 43 BC, the moderate Caesarians Aulus Hirtius and Gaius Vibius Pansa became consuls. Through the early months of the year, Antony's relations with the Senate broke down. Supported by a heterogeneous coalition including Cicero, Octavian, and large potions of the Senate, the consuls were dispatched to relieve Decimus Brutus' forces at Mutina and go to war against Antony. The consuls marched north, joined by Octavian and his private army, which had been legitimised by a grant of imperium pro praetore.
The battle
Mark Antony's plan of attack
In early March 43 BC, Hirtius and Caesar Octavian advanced along the Via Aemilia and reached Bononia; Mark Antony chose to fall back again. For the moment, he sought to strengthen the encircling front around Mutina to contain Decimus Brutus. In fact, neither Hirtius nor Octavian were seeking an immediate battle; they had two of Caesar's legions that had abandoned Antony and three legions of recalled veterans gathered by Octavian in Campania, but for the moment they were waiting for the other consul Vibius Pansa, who left Rome on 19 March, to return along the Via Cassia with four legions of recruits that had been quickly mobilized in January 43 BC.