Constantine II, the eldest son of Constantine I the Great and Fausta was Roman Emperor from AD 337 to AD 340. He was born at Arles in present day Southern France and possibly raised as a Christian. He was made a Caesar on 1 March 317 alongside his half brother Crispus as part of an agreement between Constantine and Licinius, who simultaneously promoted his own son, Licinius the Younger, to the same position.
In AD 320 and AD 321 Constantine II then held the consulship, first as the colleague of his father, then of Crispus. The fact that Constantine II was made consul, at an age too young even to be able to sign his own name, did much to support Licinius' accusation that Constantine was seeking to advance his sons at the expense of Licinius' son. A matter which was a contributing factor in the eventual break between the two Augusti.
Constantine II was involved in military expeditions from an early age on, in AD 323 he took part in Constantine I's campaigns against the Sarmatians. In AD 324, the year of Licinius' defeat, Constantine II held yet another consulship with Crispus. But in AD 326 Crispus was executed (either for treason or adultery). This left Constantine II as the senior Caesar alongside his brother and co-Caesar Constantius II who had been elevated by his father in AD 323.
Soon after the death of his half-brother Crispus in 326, at the age of 10, he was nominally put in command of Gaul. Constantine II's generals apparently won a victory over the Alamanni, since the title Alamannicus appears on his inscriptions from the year 330. In AD 332 Constantine II was sent by his father to the Danube to campaign against the Visigoths and their ruler Alaric. Naturally his was a purely ceremonial command, the actual commanding of the troops being conducted by seasoned generals rather than an unexperienced teenage, royal heir. The campaign though was very successful, a crushing victory being won over the enemy. Following this, in AD 333 Constantine II was moved to Treviri (Trier) to oversee the defence of the Rhine frontier.
In AD 335 Constantine announced the division of the empire to follow his own death, between his three sons and his nephews Dalmatius and Hannibalianus. In this division Constantine II would receive Gaul, Spain and Britain. Though the sons would defy Constantine's wishes after his death in AD 337, between them the brothers agreed to simply eliminate their cousins Dalmatius and Hannibalius. If the reason for the murder of their cousins was to not share territory with them, then Constantine II failed to secure any additional territory for himself, remaining in control of only Britain, Gaul and Spain. Though he, the eldest among the brothers, was acknowledged as the senior Augustus by the other two.
As their very accession to power was tainted by murder, it wasn't long before the brothers began to quarrel among themselves. One particular source of trouble was the bishop Athanasius. After fleeing to Treviri he was granted permission by Constantine II to return to Alexandria which was in the domain of Constantius II, who wanted him there under no circumstances. In an attempt to allay their differences, the brothers held a meeting either somewhere in Pannonia or at Viminacium. Among other things they tried to settle border disputes. But if these negotiations led to Constans gaining additional territory, then Constantine II was once again left only with Britain, Gaul and Spain.
If this settlement was unsatisfactory for Constantine II, then soon after things were made worse when Constans became ever more unwilling to accept Constantine II's claim to be the senior Augustus. In AD 340 Constantine II broke with Constans and invaded Italy, with Constans absent from Rome engaged in suppressing an uprising among the Danubian tribes. Constans hasily sent back a relatively small force to Italy, to slow the advance of the invader, while his main army could return. But this vanguard on its own successfully staged an ambush at Aquileia in which Constantine II was killed. Constans came to control his deceased brother's realm.