Magnus Maximus
In 387 the western emperor Valentinian II, together with his mother Justina and sisters, including Galla, were forced to flee to Thessalonica by the usurper Magnus Maximus, seeking Theodosius' help. Traveling to Thessalonica to meet them, the widowed Theodosius decided to marry Galla. This move consolidated his dynastic legitimacy by marriage into the house of Valentinian. In 388 Theodosius led his army into the western empire to defeat Magnus Maximus, and Justina and her other daughters returned to Italy, leaving Galla, now pregnant, in Thessalonica, where her daughter, Galla Placidia, was born.