Licinius

On April 30, 313 Licinius unified the entire Eastern Roman Empire under his rule. Although the weakest in the Tetrarchy after the death of Galerius, he wisely sided with Constantine, married Contantine's half-sister, and fought under the Christian banner of Constantine soundly defeating Maximinus Daia. A short excerpt from the text:

"Then in AD 311 Galerius died. Licinius seized the Balkan territories which had still been under the deceased emperor’s control, but could not move fast enough to also establish his rule over the territories in Asia Minor (Turkey), which were instead taken by Maximinus II Daia.

An agreement was reached by which the Bosporus was to be the border between their realms. But Constantine’s victory at the Milvian Bridge in AD 312 changed everything. Had the two sides been preparing against each other anyway, then now it was essential for either one to defeat the other in order to equal the power of Constantine.

It was to be Maximinus II Daia who made the first move. While Licinius was continuing his shrewd policy of alliance with Constantine, by marrying his sister Constantia at Mediolanum (Milan) in January AD 313 and confirming Constantine’s famous Edict of Milan (toleration of Christians and Constantine’s status as senior Augustus), Maximinus II’s forces were gathering in the east, preparing to launch an attack. Still in the winter of early AD 313 Maximinus II set across the Bosporus with his troops and landed in Thrace.

But his campaign was doomed for failure. Had Maximinus II Daia driven his troops across wintery, snow bound Asia Minor (Turkey), they were utterly exhausted. Despite their highly superior numbers they were defeated by Licinius at Campus Serenus, near Hadrianopolis, on either 30 April or 1 May AD 313."