the extortion of high pay and frequent
largesses from the emperor whom they supported. Hence, in the expectation
of fresh rewards, each army hailed as Imperator the commander who had led
it to victory over foreign foes or revolting soldiers of Rome.

*Barbarian invasions.* In addition to constant civil war, the Roman world
was exposed to all the horrors of barbarian invasions. We have already
noticed the rise of a new Persian state whose object was the
reestablishment of the empire as it had existed prior to the conquests of
Alexander the Great. Likewise on the whole extent of the northern frontier
new and more aggressive peoples assaulted and penetrated the frontier
defences. On the North Sea coast, between the Rhine and the Weser were the
Saxons whose ships raided the shores of Britain and Gaul. Facing the
Romans along the lower Rhine were the Franks, along the upper Rhine the
Alamanni, further east on the upper Danube the Marcomanni, while on the
eastern frontier of Dacia and to the north of the Black Sea were situated
the Goths and the Heruli. The withdrawal of troops from some sectors of
the frontier to meet attacks at others and the neglect of their duty by
the army corps who plunged into the maelstrom of civil war in support of
various candidates for the imperial power gave the northern barbarians the
opportunity to sweep down in destructive hordes upon the peaceful and
undefended provinces.

*Dissolution of the empire.* The natural consequence of the failure of the
imperial government to defend the provinces from hostile invasions was
that the provincials began to take measures for their own protection and
to transfer their allegiance from the Roman emperors to local authorities,
who proved a more efficient help in time of trouble. These separatist
tendencies were active both in the East and in the West and led to a
temporary dissolution of the unity of the Empire.

*Pestilence.* A third scourge which afflicted the Roman world at this
critical period was a pestilence which, originating in the East, entered
the Empire about 252 A. D., and raged for fifteen years.

*Valerian and Gallienus: 253-268 A. D.* The fortunes of the Empire reached
their lowest ebb under Valerian and his son Gallienus (253-268 A. D.). In
256, the Persians invaded Mesopotamia and Syria, and captured Antioch.
Valerian at once undertook the defence of the eastern provinces, leaving
Gallienus in charge of the West. Antioch was recovered, but