The Battle of Mursa Major, September 28 351

The Battle of Mursa was one of the bloodiest battles in Roman history. The battle took place on September 28, 351, during the Roman Civil War of 350-353. It led to the victory of Emperor Constantius II over the western forces led by the usurper Magnentius.

Background

When Emperor Constantine the Great passed away in 337 it was unclear who his successor should be. Even though his three sons, Constantine II, Constantius II and Constans, were all Caesars ruling different regions of the Empire, none of them had enough power to be named Augustus. The military, convinced that Constantine would have wanted his sons to rule a tripartite empire, killed other members of the Emperor’s family, causing a redivision of the Roman territories. As a result, Constantine was put in charge of Gaul, Hispania and Britain, Constans ruled over Italy, Africa, Dacia and Illyricum and, lastly, Constantius acquired Asia, Egypt and Syria.

However, a few years later, in 340, Constantine II attacked Constans with the aim of imposing his authority over Carthage but was killed. Constans then gained control of the provinces of the west, thus ruling over two-thirds of the Empire. In the meanwhile, Constantius was busy fighting the Persians in the east.

In 350, Constans’ generals and civilian officials, led by Magnentius, rebelled against him and murdered him. Magnentius was then proclaimed Augustus of the west and quickly marched toward Italy. In the meanwhile, Vetranio, Constans’ lieutenant in Illyricum, was also declared Augustus by his troops. Constantius, who was already fighting a war against the Sassanians, waited for them to retreat from Nisibis to march his army to Serdica to deal with the situation. There, he met Vetranio, who agreed to abdicate. Constantius then set out west to face Magnentius.

The Battle of Mursa

In September 351, Constantius intercepted Magnentius while he was besieging Mursa, near the province of Pannonia (modern Osijek, Croatia). As a result, the latter was forced to retreat and formed up his army, which consisted of 36,000 men, in the northwest of Mursa, close to the Drava River. In the meanwhile, Constantius also positioned his army and decided to send his praetorian prefect, Flavius Philippus, with a peace offer to avoid the battle. However, Magnentius refused the proposal.

The battle, which took place on September 28, was long and lasted until nightfall, when Constantius’ army claimed victory and Magnentius was forced to flee west into Italy, avoiding capture on the way. It was also one of the most brutal battles in the history of the Roman Empire, as it resulted in the loss of 54,000 lives (Constantius’ army lost 30,000 and Magnentius’ 24,000). Still, Constantius himself did not take part in the battle and heard of his victory from the bishop of Mursa. Soon after this, the Emperor claimed that the victory had been possible thanks to God’s aid. 

Aftermath

After his victory, Constantius decided not to go after Magnentius and spent the next months retaking towns still loyal to the latter. It would not be until two years after the battle, in 353, that the two of them would confront each other again at the Battle of Mons Seleucus, where Constantius’s victory would lead Magnentius to take his own life.

Nowadays, the battle is considered by historians as a pyrrhic victory of Constantine. However, at that time, the casualties of the Battle of Mursa were considered by many Roman historians as extremely harmful to the Empire, as it left the army so weakened that it was not able to fight the barbarian incursions.