The Beginning of the End
It was under Marcus Aurelius (161-180 AD) that Rome began to suffer conflict, war and other unrelated problems of famine and disease. Marcus Aurelius’ 19-year-old son Commodus was known for decadence, cruelty and above all, incompetence; he was eventually killed by his own advisors and a period of civil war began.
Septimius Severus restored peace but the Severan dynasty (the last hereditary rulers) was disturbed by highly unstable family relationships, as well as constant political turmoil. From 235 A.D. on, generals were crowned Emperor by their troops and the next fifty years saw 41 Emperors.
When Diocletian came to power in 284 A.D., the government of the empire was divided between the two senior emperors, the augusti, and their juniors and designated successors, the caesares.
Diocletian and his successor, Galerius, held power in the east while the west was ruled by Maximian and Constantius – the four of them were known as the Tetrarchy. The unity and stability of the Roman empire suffered greatly.