Magnentius was accepted as emperor in Gaul, Britain and Spain and acquired Italy and Africa as well. He didn't manage to get the Danube armies, because the commander of the Danube armies, Vetranio, was declared emperor as well. Vetranio declared in favour of Constantius II and retired. In 351, the bloody Battle of Mursa Major occured between Magnentius and Constantius II in Pannonia, near the border of Italy. Magnentius lost and hastily withdrew from Italy to Gaul.
Italy was lost to Constantius II, but Magnentius managed to maintain his position in the rest of his realm. In 352, Constantius II had to deal with an invasion of the Sarmatians and Magnentius with one of the Alamanni and Franks in the Upper Rhine region. In 353, Magnentius lost the Battle of Mons Seleucus in the Alps on the border of Italy and Gaul, and committed suicide by falling in his sword.