Decentius vs Theodosius the Great

After Magnentius usurped the Western Roman throne, he appointed his brother Decentius as Caesar. Decentius was given command of Gaul and tasked with defending the Rhine frontier against Germanic tribes.

Decentius's forces failed to prevent Alemanni incursions into Gaul, leading to significant devastation. This military failure weakened Magnentius's position and undermined confidence in the usurper regime.

After Magnentius was defeated by Constantius II at the Battle of Mons Seleucus, Decentius hanged himself. His suicide ended the usurper dynasty and restored the Western Roman Empire to Constantius II's control.

Theodosius issued the Edict of Thessalonica, declaring Nicene Christianity the official state religion of the Roman Empire. All other Christian sects were deemed heretical, and pagan practices were increasingly suppressed.

Theodosius ordered a massacre in Thessalonica after a riot killed a Roman official. Thousands of citizens were killed in the circus. Bishop Ambrose of Milan excommunicated Theodosius until he performed public penance.

Theodosius defeated the usurper Eugenius and his general Arbogast at the Battle of the Frigidus. The victory reunited the Roman Empire under Theodosius's rule for the last time before its permanent division.

Upon his death, Theodosius divided the Roman Empire between his sons: Arcadius received the East and Honorius the West. This division became permanent, leading to the separate development of the Byzantine and Western Roman Empires.