Constantius II was
born in Illyricum in August AD 317, the son of Constantine the Great and
Fausta, and was proclaimed Caesar in AD 323.
In AD 337, at the
death of his father Constantine, he acceded to the throne together with
his two brothers Constantine II and Constans. But this accession by the
three brothers was tainted by the murder of their cousins Dalmatius and
Hannibalianus, whom Constantine had also intended as joint heirs. These
murders are believed to have been masterminded by Constantius II.
In the eventual
division of the empire between the three brothers, Constantius II received
the east as his dominion, which largely corresponded with what his father
had originally intended for him. It therefore appears that Constantine the
Great had held Constantius II in high esteem, and had deemed him most able
to deal with the menace of the Persians in the east.
Almost at once after
the news of Constantine's death the Parthian King Sapor II (Shapur II)
attacked the empire, with which he had been at peace for four decades.
In AD 338
Constantius II granted Constans control over his European territories,
Thrace and Constantinople. Perhaps he thought it necessary to satisfy the
ambitions of his younger brother by granting him more land thereby
securing his western border in order to be able to freely engage with
Sapor II in the east.
Constantius II, much
like his father before him, was deeply involved in theological matters.
Though he supported Arianism, a form of Christianity including aspects of
Greek philosophy, which the 'Nicene Creed' brokered by his father
had outlawed as heresy. Had Arius been excommunicated by Constantine's
Council of Nicaea, then Constantius II rehabilitated him posthumously.
The conflict in the
east with Sapor II concentrated almost entirely on the strategic
fortresses of Mesopotamia. Three times Sapor II besieged the fortress town
of Nisibis, but failed to take it. Then by AD 350 the Parthian king needed
to agree a truce with his Roman foe, in order to deal with tribal problems
in the east of his own empire.
Constantius II had become the sole legitimate Roman emperor. Had
Constantine II declared war on his brother Constans in AD 340, he died in
the attempt of invading Italy. Meanwhile Constans himself had been slain
when Magnentius had usurped his throne in AD 350.
Things hung in the
balance for a while, as the all-important Danubian legions could simply
not make their minds up which one of the two rivals to support. And so, in
a strange twist of fate, they chose niehter leader, but instead hailed
their own 'Master of Foot', named Vetranio, as their emperor. Though
rebellious as this might seem at first sight, it appeared to be in
accordance with Constantius II. His sister Constantina was in Illyricum at
the time and appeared to have supported Vetranio's elevation.
preparing for the fight with Magnentius in the west, raised his 26
year-old cousin Constantius Gallus to the rank of Caesar (junior emperor)
in order to have him take charge of the administration of the east whilst
he would be commanding his armies.
What followed in AD
351 was an initial defeat by Magnentius at Atrans, as Constantius II tried
to advance and force his way into Italy. As Constantius II retreated
Magnentius sought to follow up his victory but was heavily defeated at the
gruelling battle of Mursa in Lower Pannonia, which cost over 50'000
soldiers their lives. It was the bloodiest battle of the fourth century.
to Italy, seeking to rebuild his army.
Constantius II was
left as the sole emperor of the Roman empire. But news reached him of his
cousin Gallus' behaviour in the eastern provinces. Had he successfully
dealt with rebellions in Syria, Palaestina and Isauria, Gallus had also
ruled as an utter tyrant, causing all manner of complaints to the emperor.
Next, Constantius II needed to deal with the Franks who had broken
over the border during his struggle with Magnentius. So confident was the
Frankish leader Silvanus that he proclaimed himself emepror at Colonia
Agrippina. Silvanus' murder was soon arranged, but the ensuing confusion
saw the city sacked by German barbarians.
therefore left the Mesopotamian frontier and marched his troops west,
seeking to deal with the usurper.