In A.C. 305 Diocletian relinquished power altogether, forcing Maximian
to abdicate with him; Galerius and Constantius Chlorus thus obtaining
the coveted title of Augustus, and sharing the supreme power.

Galerius now ranked first, however; for it was to the ruler of
Illyricum and not to that of Gaul that Diocletian gave the power of
appointing Caesars to govern Italy and the East.

Constantius Chlorus died in Britain A.C. 306, the year after Diocletian
abdicated; and Galerius, who had married a daughter of Diocletian,
naturally thought that under the circumstances he ought to become sole
emperor.

The legions of Gaul, however, proclaimed the son of Constantius Chlorus
as Augustus in his stead; and as Constantine thus became ruler of Gaul
and a power to be reckoned with, Galerius thought it best to give way
so far as to grant Constantine the inferior title of Caesar.

Soon afterwards Galerius conferred the title of Augustus upon Severus;
and a little while after that the Eternal City was lost to Galerius
through the revolt of his son-in-law Maxentius, the son of Maximian.

The Senate of Rome then asked Maximian to re-assume the purple, and he
and Maxentius shared the power between them, both taking the title of
Augustus.

Upon this Severus at the request of Galerius marched upon Rome. He was,
however, defeated and slain.