Emperor Diocletian’s Tetrarchy designed to reform the Roman Empire after the Third Century Crisis was short lived, and followed by the rise of Constantine the Great.
During the last 15 years of the Third Century Crisis of the Roman Empire, Emperors such as Aurelian, Tacitus and Diocletian led the Empire out of chaos.
In the last quarter of the third century the Roman Empire began crumbling as Emperors were unable to maintain its borders against barbarian incursions.
During the first half of the third century AD, the Roman Empire was ruled by a rapid succession of Barrack Emperors, elected and assassinated by their own troops.
Procopius, spied for his cousin Emperor Julian on the Persians, but when the time came, he seized the throne from Valens in Constantinople, to become emperor.