Sextus Martinianus in Wikipedia

Sextus Marcius Martinianus (usually rendered in English as Martinian; died 325) was Roman Emperor from July to September 18, 324. He had been appointed co-emperor by Licinius. Elevation - In 324 the second civil war between Licinius and Constantine I was at its height, and Licinius was losing. Because of this war he decided to replace Constantine (in name only) as western Augustus. As his replacement he named Martinian co-emperor, as he had previously appointed Valens[1] during his earlier war with Constantine. Prior to his elevation, which took place some time after the Battle of Adrianople (July 3, 324), Martinian was serving as magister officiorum at Licinius' court. Military activities - Following his defeat at Adrianople Licinius sent Martinian, with an army including Visigothic auxiliaries,[2] to Lampsacus (on the Asiatic shore of the Hellespont or Dardanelles) to prevent Constantine from crossing from Thrace into Mysia and Bithynia in Asia Minor. A naval battle in the Hellespont resulted in the destruction of Licinius' navy by Constantine's eldest son Crispus. Following this defeat Licinius withdrew his forces from Byzantium, which was being besieged by Constantine, to Chalcedon on the Asiatic shore of the Bosphoros. Constantine then crossed over to Asia Minor, using a flotilla of light transports in order to evade the forces of Martinian.[3] Licinius recalled Martinian from Lampsacus to reinforce his main army.[4][5] On September 18 Licinius was defeated for the last time at the Battle of Chrysopolis. Fate - Due to the intervention of Flavia Julia Constantia, Constantine's sister and also Licinius' wife, both Licinius and Martinian were initially spared, Licinius being imprisoned in Thessalonica, Martinian in Cappadocia. However, Constantine seems to have soon regretted his leniency as both men were subsequently executed, probably in the spring of 325.[6]