GALLUS, COSTANZO (Flavius Iulius Constantius Gallus). — Caesar from 351 to 354, son of Julius Constantius, half-brother of Constantine the Great, and of Galla, born at Massa Marittima in 325-26, died near Pola on the day of 354. Having escaped the massacres of 337 after the death of Constantine, he was taken, together with his brother Julian, to Nicomedia and entrusted to the Arian bishop Eusebius. In 345-46 he was transferred to Macellum near Caesarea in Cappadocia.
Suddenly in 351, he was created Caesar by Constantius II and entrusted with defending the eastern frontiers of the Empire from Persian incursions. He then married the Emperor’s sister, Constantina, and fixed his residence at Antioch in Syria. In his administration he proved cruel, punishing entire cities with bloody massacres and destruction to suppress insurrectionary movements; while he lived in dissipation and baths, the true interests of the Empire were neglected. With his connivance, the people assassinated Dominian, the imperial favourite, and Manzius, the quaestor whom Constantius had placed beside him to assist in and oversee his government. Constantius then recalled him to Milan under the pretext of holding discussions, but upon his arrival in Istria, Gallus was arrested, summarily tried, and executed in the city of Flanona near Pola.