Unhappy over the distribution of the provinces, he invaded Italy in 340 AD, only to be killed in an ambush by Constans' troops.

Constans grew unpopular with the army, leading to a military conspiracy which overthrew and killed him in 350 AD.

The situation changed dramatically when his troops encountered Constantius' cataphract cavalry at the Battle of Mursa on 28 September 351.

The fighting involved 95,000 troops and left 55,000 casualties in one of the bloodiest battles in Roman history.

Magnentius decided to retreat into Gaul, where Constantius defeated him again at Mons Seleucus on 3 July 353.