In the mid-to-late 290s the Imperial Tetrarchy was at war on multiple fronts. In the west Constantius undertook the reconquest of Britain, while in the east, Galerius fought a newly hostile Sassanid Empire.

In 293 AD Diocletian and Maximian invited Constantius and Galerius to share in their Imperial burdens, forming what we today call the Tetrarchy.

Immediatly after becoming the undisputed Emperor in 285, Diocletian elevated Maximian to serve as his Imperial colleague.

The Crisis of the Third Century finally ended with the mini dynasty of Carus and his two sons. In 284 Diocletian rose to power, ushering in a new age in Roman history.