Flavius Arinthaeus

Flavius Arinthaeus (died AD 378) was a Roman politician and military officer, serving the emperors Constantius II, Julian the Apostate, Jovian and Valens. He was appointed consul in AD 372 alongside Domitius Modestus.

Early career
Beginning his service as a career military officer, in AD 354/5 Arinthaeus served as a tribunus in Raetia. He belonged to one of the legions which accompanied the emperor Constantius II on his campaign against the Alemanni, where Arinthaeus was instrumental in securing a victory against the enemy in difficult circumstances. Rising through the ranks, he became one of the palace court officials under Constantius. In AD 361, he accompanied Constantius in the emperor’s march against the Caesar Julian in Gaul.

Arinthaeus is next mentioned in AD 363, where as Comes rei militaris, he accompanied the emperor Julian on his Persian campaign. He was put in charge of the cavalry on the left wing during the advance into Asuristan, and he repulsed at least one attack by the Persians on their way through. He later commanded an infantry force during Julian’s engagement outside of Ctesiphon, where he ravaged the countryside and pursued what Persians he could find.

With Julian’s death in Mesopotamia, Arinthaeus and a number of other court officials who had served under Constantius began looking among their number for a replacement, but were opposed by Julian’s Gallic officers. Eventually Arinthaeus and the rest agreed to the elevation of Salutius, who refused to accept the imperial nomination, and they were forced to accept the elevation of Jovian. Jovian kept much of Julian’s senior staff intact, and one of his first acts was to send both Arinthaeus and Salutius to negotiate a truce with the Sassanid king Shapur II. The negotiations lasted around four days, and it saw Arinthaeus hammer out a compromise whereby the Romans gave up five satrapies on the eastern side of the Tigris River, and abandoned control of eastern Mesopotamia, while retaining all of western Mesopotamia. Roman influence was also restricted in and around Armenia. On their way back from the east, Jovian dispatched Arinthaeus to Gaul, where he was ordered to confirm Jovinus as the Magister equitum there.

Service under Valens
Arinthaeus supported Valentinian I’s accession as emperor in AD 364, and was transferred to the court of Valentinian’s brother, Valens at Constantinople. As Dux, he was involved in suppressing the revolt of Procopius in AD 366. Valens sent him to the border of Bithynia and Galatia with an army against Hyperechius, an ally of Procopius. Arinthaeus convinced the army of Hyperechius to abandon Procopius. Arinthaeus was then appointed Magister peditum after the defeat of Procopius, a position he held until AD 378.

Arinthaeus then accompanied Valens during the First Gothic War from AD 367 to 369. In 368, he was dispatched to harass the Thervingi in Gothia, with his soldiers rewarded with a gold coin for every barbarian head their brought back. The following year, AD 369, Arinthaeus was asked to negotiate a peace with king Athanaric, before being immediately dispatched to the Persian frontier. Spending the end of 369 and early 370 repairing the road between Amaseia and Satala, he then marched into Armenia with an armed force to re-install Papas (Pap) on the throne of Armenia and to help him resist the incursions of the Sassanid Empire. His presence there forced Shapur II to call off his planned invasion, and curtailed Papas’ attempts to come to an agreement with the Sassanid king. Arinthaeus remained in Armenia throughout AD 371.

During the following year (AD 372), Arinthaeus was appointed consul posterior, serving together with Domitius Modestus. He supported Traianus after Traianus’ failure to achieve victory at the Battle of the Willows in AD 377.

Arinthaeus died in AD 378, while still in the prime of life. He was baptised a Christian on his deathbed. He was married and had at least one daughter, he was a correspondent of Basil of Caesarea, and was alleged to have confronted the emperor Valens over his Arianism.