Justina (Iustina; c. 340 – c. 388) was a Roman empress. She was initially the wife of the rebel emperor Magnentius (350-353) and was then married to Valentinian I (364-375), with whom she had four children, including the emperor Valentinian II (375-392) and the empress Galla (387-394). Possibly a relative of the Constantinian dynasty (293-363), she was Valentinian's second wife after Marina Severa, and step-mother of the augustus Gratian (367-383) and the mother-in-law of the augustus Theodosius I (379-395). Her infant son Valentinian was made emperor shortly after her husband's death in November 375. According to Late Antique ecclesiastical history, Justina was an Arian Christian, and began to promote this christology after her husband died, bringing her into conflict with Ambrose, the Nicene Christian bishop of Mediolanum (Milan). In 387, fleeing from the invasion of the Italian Peninsula by the emperor Magnus Maximus (383-388), Justina took her children to the Balkans – including the child-emperor Valentinian II – and secured the intervention of the eastern emperor Theodosius in the civil war by marrying her daughter Galla to him at Thessalonica. Afterwards, Theodosius attacked and defeated Magnus Maximus, ending the civil war, during which time Justina herself apparently died. Justina was a daughter of Justus, governor of Picenum under Constantius II. According to Socrates of Constantinople: "Justus the father of Justina, who had been governor of Picenum under the reign of Constantius, had a dream in which he seemed to himself to bring forth the imperial purple out of his right side. When this dream had been told to many persons, it at length came to the knowledge of Constantius, who conjecturing it to be a presage that a descendant of Justus would become emperor, caused him to be assassinated." Justina had two known brothers, Constantius and Cerealis. One of her daughters was named Galla. In La Pseudobigamie de Valentinien I (1958), J.