 Theodosius also betrothed him to his own daughter Licinia Eudoxia (whom Valentinian would eventually marry in 437 when he was 18).It was only in the following year, after Joannes had been defeated in a combined naval and land campaign, that Valentinian was installed by the eastern "patricius et magister officiorum" Helion as Western Emperor in Rome, on October 23, 425, at the age of six.Given his minority, the new "Augustus" ruled under the regency of his mother Galla Placidia, one of whose first acts was to install Felix as the Magister utriusque militiae in the west.