since the praetorian prefect and the emperor's counsellors met him and demanded that he turn over the basilica. When Ambrose was summoned to be punished to the Imperial palace, the orthodox populace rioted, and Gothic troops were prevented by the arch-bishop himself, standing in the doorway, from entering the Basilica. Rufinus, influenced by Ambrose's writing, claimed that when Ambrose was found to have determinedly infracted the new laws, Justina persuaded Valentinian to have him banished, and Ambrose was forced to barricade himself, with the enthusiastic backing of the people, within the walls of the Basilica. Rufinus continues that the imperial troops besieged him, but Ambrose held on, reinforcing the resolution of his followers by allegedly unearthing, beneath the foundations of the church, the bodies of two ancient martyrs. Later, Magnus Maximus was purported to have used the emperor's heterodoxy against him. Maximus indeed wrote a scathing letter attacking Valentinian for plotting against God. In 386 to 387, Maximus crossed the Alps into the Po valley and threatened Milan. Valentinian II and Justina fled to Theodosius in Thessalonica. The latter came to an agreement, cemented by his marriage to Valentinian's sister Galla, to restore the young emperor in the West. In 388, Theodosius marched west and defeated Maximus. Although he was to appoint both of his sons emperor (Arcadius in 383, Honorius in 393), Theodosius tolerated Valentinian, and made him a subordinate ruler to him. Reign from Vienne (388–392) After the defeat of Maximus, Theodosius remained in Milan until 391. Valentinian took no part in Theodosius's triumphal celebrations over Maximus. Valentinian and his court were installed at Vienne in Gaul, while Theodosius appointed key administrators in the West and had coins minted, which implied his guardianship over the 17-year-old. Justina had already died, and Vienne was far away from the influence of Ambrose. Theodosius's trusted general, the Frank Arbogast, was appointed magister militum for the Western provinces (bar Africa) and guardian of Valentinian. Acting in the name of Valentinian, Arbogast was actually subordinate only to Theodosius. While the general campaigned successfully on the Rhine, the young emperor remained at Vienne, in contrast to his warrior father and his older brother, who had campaigned at his age. Arbogast's domination over the emperor was considerable, and the general even murdered Harmonius, a friend of Valentinian suspected of taking bribes, in the emperor's presence. The crisis reached a peak when Arbogast prohibited the emperor