Justin, the commander of the palace guard, had secured the imperial throne on the death of Emperor Anastasius in July 518.
Unlike his predecessor, Justin supports orthodoxy, and in 518-519 had been instrumental in ending the Acacian schism with Rome and persecutes the dissident Monophysites.
In 523, he also issues an edict against Arianism.
This offends the Arian king Theodoric of the Ostrogoths, who forces Pope John I to visit Constantinople to plead for a mitigation of the edict.
Justin then grants some concessions to the Arians but not enough to satisfy Theodoric.
In the East, the struggle with Persia makes it important for Constantinople to retain control of the small Christian kingdom of Lazica (modern Colchis, a region in Georgia), to secure allies in Mesopotamia and southern Syria, and to counter Persian penetration into Arabia by an understanding with Ethiopia.
On the northern frontier, the Slavs are already crossing the Danube River and troubling the Balkan provinces, and Justin proves unable to repel them.
