The Origins of Christianity and the Decline of the Roman Empire 105great masterworks of history, he was at best only half
right. Neither Christianity nor pagan immorality con-
tributed to the catastrophe that befell the western em-
pire in the fifth century A.D. While the “barbarians”
clearly played a major role, they were little more bar-
baric than some of the emperors they replaced.
The true cause of imperial decline was instead a
generalized crisis whose basic outlines had become
apparent as early as the second century. When Mar-
cus Aurelius died in A.D. 180, an army of more than a
half million men patrolled a border of several thou-
sand miles. Within that border the pax romanawas
broken only by occasional riots, but beyond it, pow-
erful forces were gathering. Germanic tribes—Franks,
Alemanni, Burgundians, and others in the west;
Visigoths and Ostrogoths to the east—pressed
against the Rhine and Danube frontiers. For reasons
that remain unclear, their populations had grown be-
yond the available food supply in central Europe.
Behind them, on the eastern steppes, other peoples
with similar problems pushed westward into the
German tribal lands. Population movements on this
scale created intolerable pressure when they came up
against settled borders. The Germans did not hate
Rome. They sought only to settle within it. They
were hard, determined fighters whose grasp of strat-
egy was anything but primitive. In fighting them,
Marcus Aurelius faced unpredictable attacks in force
delivered along a perimeter too extensive to be
manned completely by the legions. His bitter strug-
gle with the tribes was an inkling of things to come.
To the east, the Romans faced a more conventional
foe. The Parthian Empire was a sophisticated territorial
state based, like Rome, on taxes and tribute. It fought
until it exhausted its resources and then made peace un-
til its economy could recover. The pressure it exerted
on the eastern borders was therefore sporadic rather
than constant, but it was nevertheless severe. Rome de-
feated the Parthians in A.D. 198 and briefly annexed
Mesopotamia. This success was followed by a change
of dynasty in the eastern kingdom. An Iranian prince,
Ardashir I, overthrew the Parthians and established the
Sassanid dynasty, which lasted until the Arab conquests
of the seventh century. Determined to recapture
Mesopotamia, he and his successors launched a series
of wars that further depleted the Roman treasury,
weakened the eastern provinces, and ended in 260 with
the capture of the emperor Valerian.
The Roman economy could not sustain this level of
military commitment, and the third century was one of
almost unrelieved crisis. The prosperity of Augustan
times had been in some respects artificial. Much of it
was based on the exploitation of new wealth derived
from imperial expansion. When the expansion stopped,
that wealth was not replaced. Beneath the glittering
surface of the early empire, the economy remained
stagnant. The mass of slaves, tenant farmers, and unem-
ployed citizens consumed little. Their productivity wasCHRONOLOGY 6.1
The Important Roman Emperors
27 B.C.–A.D.14 Augustus
A.D. 14–37 Tiberius
37–41 Caligula
41–54 Claudius
54–68 Nero*
68–69 The year of the four emperors
69–79 Vespasian
79–81 Titus
81–96 Domitian*
96–98 Nerva
98–117 Trajan
117–138 Hadrian
138–161 Antoninus Pius
161–180 Marcus Aurelius*
180–192 Commodus
193–211 Septimius Severus
211–217 Caracalla
218–222 Elagabalus
222–235 Severus Alexander
249–251 Decius*
253–260 Valerian*
253–268 Gallienus
268–270 Claudius II Gothicus
270–275 Aurelian
284–305 Diocletian*
306–337 Constantine
337–361 Constantius II
361–363 Julian the Apostate
364–375 Valentinian
364–378 Valens
379–395 Theodosius
*Launched major persecutions of the Christians.