text: This ruler tried to broker peace on a barren plain called Campus Serenus, but on being rebuffed, his army won the Battle of Tzirallum, though shortly afterwards he was defeated in battles at Cibalae and on the plain of Mardia.
full_question: This ruler tried to broker peace on a barren plain called Campus Serenus, but on being rebuffed, his army won the Battle of Tzirallum, though shortly afterwards he was defeated in battles at Cibalae and on the plain of Mardia. This ruler was granted the territory of Pannonia at the Conference of Carnuntum, and expanded his power from that base. His fleet of ships was busted up by the general Flavius Crispus at the Battle of the Hellespont, after which he met his final defeat at Chrysopolis and was kept as prisoner at Thessalonica until being hanged the following year. He ascended to the throne solely due to his friendship with Galerius, and in the midst of fighting against his main rival Maximinus Daia, he celebrated his wedding to Constantia, which was the occasion for the formal issuance of the Edict of Milan. For 10 points, name this Roman emperor who, after defeating Maxentius and Maximinus, launched a failed civil war against Constantine the Great.
first_sentence: This ruler tried to broker peace on a barren plain called Campus Serenus, but on being rebuffed, his army won the Battle of Tzirallum, though shortly afterwards he was defeated in battles at Cibalae and on the plain of Mardia.
raw_answer: Licinius [or Valerius Licinius Licinianus]