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 Vibius Pansa Caetronianus, aided by his fellow consul Aulus Hirtius and the untested Caesar Octavian (the future Augustus).
The consul Mark Antony, the erstwhile close ally of Julius Caesar had briefly dominated Rome shortly after the assassination of Julius Caesar, but had gradually lost power since the summer of 44 BC due to the increasing popularity among veterans and the Caesarian faction of the dictator’s young heir, Caesar Octavian, and the rebuilding of a Pompeian Senatorial faction led by Marcus Tullius Cicero. The coalition against Mark Antony also included some of Caesar’s murderers, including Decimus Brutus, who had taken control of Gallia Cisalpina with three legions in April 44 BC.
By June of 44 BC the situation in Rome became more difficult for Mark Antony: Caesar Octavian was winning support, the Senate appeared hostile, and two of Antony’s best legions defected to the young Caesar, despite Antony’s appeals and threats of punishments. On 28 November 44 BC, Mark Antony decided to take the initiative and, with the four legions remaining faithful to him, rushed north against Decimus Brutus, who, by the end of the year, was besieged in Mutina.
On 1 January 43 BC, the moderate Caesarians Aulus Hirtius and Gaius Vibius Pansa became consuls, and from that moment on, especially thanks to Cicero’s propaganda campaign with his Philippics, a heterogeneous coalition against Antony took shape and gathered strength. During a session of the Senate, Cicero succeeded in legalizing Caesar Octavian’s actions in gathering an army of veterans at Arretium; the young man was assigned the rank of propraetor and the task of marching against Antony. A delegation of three senators was sent to seek an agreement with Antony, who was still besieging Decimus Brutus in Mutina, but at the same time new legions of recruits for war were being raised.
In early March 43 BC, Hirtius and Caesar Octavian advanced along the Via Aemilia and reached Bononia; Mark Antony chose to fall back. 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.
When Mark Antony became aware of the approach and imminent concentration of his enemies, he set out to take the initiative and move on to the attack as soon as possible. Antony decided to leave part of his forces under the command of his brother Lucius Antonius to hold Decimus Brutus in check, and engage Hirtius and Octavian with a feigned attack on their camp, while moving against Pansa’s troops under cover of darkness with his best legions.
The Legio Martia and Vibius Pansa’s recruits suddenly stood threatened in front of and alongside Antony’s legions. The experienced legionaries did not lose their cohesion, but accepted battle after sending back the cohorts of recruits that were deemed unsuitable for the fight by the Caesarian veterans of the Martia. While the praetorian cohorts of Antony and Caesar Octavian fought sharply along the main road, the Martia veterans split into two parts and, under the command of Pansa and Carfulenus, ran into the marshes to join the battle.
The fighting between the Caesarian veterans of both parties was dramatic and bloody; in his history, Appian describes the particular bitterness of the two parties to a fratricidal struggle. Both sides believed that they could obtain a decisive victory, as the veterans’ military pride increased the fury of the fight. The clash between the Caesarian veterans on the two sides took place in a dark silence: without battle-cries or exhortations, the legionaries fought hand-to-hand in a frontal collision between their massed ranks in the swamps and valleys. The legionaries’ fratricidal carnage was interrupted only by short breaks used to tighten their formations. The veterans knew their job well; without the need for encouragement, they continued the struggle with tenacity and obstinacy. The mutual slaughter with drawn blades impressed Pansa’s inexperienced recruits, who watched the deadly and silent action of the Caesarian legionaries on both sides.
The battle finally turned to the favour of Antony’s forces: in the centre along the Via Aemilia, Antony and Silanus‘ praetorian cohorts prevailed in a brutal clash with Caesar Octavian’s praetorian cohorts, which were completely destroyed. In the marshes to the right of the highway, the legionaries of the Martia, who were isolated some 500 paces in advance, were threatened by Antony’s Moorish cavalry; Decimus Carfulenus had fallen mortally wounded, and the veterans began to fall back while still repulsing the cavalry’s assaults.
Mark Antony’s legionaries hastened to pursue the enemy, inflicting heavy losses on the veterans and new conscripts as they fled back towards their camp. The survivors of the Legio Martia actually remained outside the camp and by their presence dissuaded the Antonian legionaries from attacking further. The remnants of the Senatorial legions were virtually trapped inside their camps, and the Antonian veterans would likely force them to surrender in the event of prolonged siege, but Mark Antony was concerned about losing time, fearing that the situation would deteriorate in Mutina in case Hirtius and Octavian’s legions sought to break his siege there. Antony therefore felt that he could not stay on the battlefield and decided to return with his forces to the city.
Hirtius decided at once to march to Pansa’s aid with the Legio IV Macedonica, the other Caesarian legion that had defected at Brundisium. These fresh troops moved quickly and, in the late afternoon of 14 April 43 BC, came unexpectedly into contact with the legions of Mark Antony who, exhausted after the tough battle, marched in the direction of Mutina in poor order and heedless of danger in their front. The IV Macedonica led by Aulus Hirtius, experienced and well-rested, came to the attack in tight formation against Antony’s disorderly and tired troops. Despite attempts at resistance and instances of bravery, the Antonian legions could not withstand the assault, but suffered heavy losses and disintegrated under the attacks of Hirtius’ Caesarian. Two eagles and sixty other standards were captured by their enemies. Only with great difficulty could Mark Antony rally the remnant with the help of the cavalry, which managed to round up the soldiers during the night and bring them back to camp near Mutina. Aulus Hirtius, hindered by darkness and wary of being lured into a trap, chose not to pursue the defeated Antonian legions. Thus ended the long battle of Forum Gallorum. The marshes were covered with arms, trunks, horse remains, corpses of legionaries of the two sides perceived in the alternate fights.
Although Caesar Octavian’s direct role on the day of the battle, 14 April 43 BC, had been minimal, he was acclaimed as imperator on the field by his troops.
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