Caesar

On 1 March 317, he was made caesar.^[3][1] Constantine II usually resided with his father, such as accompanying him on his campaign against the Sarmatians in 323,^[4] until his own court was installed at Trier in 328.^[5] An inscription dated to 328-330^{[lower-alpha 2]} records the title of Alamannicus, indicating that his generals won a victory over the Alamanni.^[3] His military career continued when Constantine I made him field commander during the 332 winter campaign against the Goths.^[3] The military operation was successful and decisive, with 100,000 Goths reportedly slain and the surrender of the ruler Ariaric.^[7] Festival games were initiated in Rome to celebrate the Caesar’s role in the successful military campaigns, in a public advertisement of his capability to rule.^[8] He was married prior to 336, although his wife’s identity remains unknown.^[9]

While Constantine I had intended for his sons to rule together with their cousins Dalmatius and Hannibalianus, soon after his death in May 337 the army slaughtered almost all of their male relatives, including Dalmatius and Hannibalianus.^[10] Burgess observed from numismatic evidence that Constantine II and his brothers “not only seem not to have fully accepted the legitimacy of Dalmatius and viewed him as an interloper, but also appear to have communicated with one another on this point and agreed on a common response.”^[11]

In what seemed to be an attempt to distance themselves from the massacre,^[12] the three brothers proceeded to print coins of Theodora, whom their murdered relatives had been descended from.^[10] The evidence indicates that Constantine II was the one responsible for designing and producing the coinage at the start, as well as convincing his brothers to do the same.^[13] Woods considered it to suggest that he was more sympathetic to Theodora’s memory than his brothers,^[14] possibly because his wife may have been a granddaughter of Theodora.^[9]

In June 337, before he was named emperor, Constantine had already begun attempting to assert his seniority.^[15] He issued an order allowing the exiled bishop Athanasius to return to Alexandria, claiming to be carrying out the unfulfilled intentions of his father.^[3][16]

Augustus

The three brothers were not named as Augusti until 9 September 337,^[1] when they gathered together in Pannonia^[3] and divided the Roman territories among themselves. Constantine received Gaul, Britannia and Hispania.^[17][18] Unlike his younger brothers, he gained little from Dalmatius’ removal.^[19]

Constantine was evidently left unsatisfied with the results of their meeting,^[20][8] seemingly believing that his age granted him some sort of seniority in the imperial college^[21] and, by extension, control over the dominion of his youngest brother Constans, who was still a teenager in 337.^[16][22] Even after campaigning successfully against the Alamanni in 338, he continued to maintain his position.^[16][23][24] The Codex Theodosianus recorded Constantine’s legislative intervention in Constans’ territory through issuing an edict to the proconsul of Africa in 339.^[16][25]

In 340, Constantine launched an invasion into Italy to claim territory from Constans.^[16][3] Constans, at that time in Naissus,^[20] sent a number of troops to confront him, and Constantine was killed in an ambush near Aquileia.^{[16][26][lower-alpha 3]} Constans then took control of his deceased brother's realm, who seem to have been largely unaffected by their change in ruler.^[28] After his death, Constantine was subjected to damnatio memoriae,^[16] which his other brother Constantius II also followed.^[22]