Arbitio

Arbitio (fl. 354-366) was a Roman general (magister militum) and Consul who lived in the middle of the 4th century.

In the Reign of Constantius II
He was a general of Constantine I and reached the highest military positions in the Roman army under his son and successor Constantius II and became magister equitum (commander of the cavalry). In 355 he was made consul together with Quintus Flavius Maesius Egnatius Lollianus.

Arbitio was a well trusted courtier of Constantius and some modern historians have suggested he was his military strongman.

Arbitio intrigued against Claudius Silvanus, Ursicinus and Barbatio and played a role in their downfalls. Historian Ammianus Marcellinus says he was "keen and eager in plotting treachery", and describes him as "fickle flatterer" to Constantius II.

In the Reign of Julian
After the death of Constantius in 361, he was appointed chairman of the Chalcedon tribunal by the new Emperor Julian. In this function he was responsible for the conviction of Paulus Catena and many ministers and followers of Constantius. Arbitio did not take part in the Persian campaign of Julian, but instead retired to live as a private citizen.

In the Reign of Valens
A couple of years after Julian's death, a maternal relative of Julian named Procopius made an attempt to usurp the Eastern Empire. Arbitio himself was courted by this Procopius. However, Arbitio ignored the summons of Procopius, who, in response, confiscated his properties. This action led Arbitio to join Procopius' opponent, Valens, who appointed Arbitio "ad hoc magister militum". During the subsequent campaign, Arbitio was able to convince Gomoarius, a general in the army of Procopius and an old friend of Arbitio, to desert to Valens. Eventually, Procopius was deserted by most of his troops, and attempted to hide from his fate, but was tied up by two of his attendants and turned over to Valens, who had both the usurper and his betrayers executed.

What happened to Arbitio after this time is unknown, although it is reasonable to assume that he retired, and subsequently died without taking any further part in matters of state.