Germanic tribes that wanted to loot Gaul. Aft er about four
years of war, Tetricus’s reign was ended in a battle in northern
Gaul by Roman emperor Aurelian (r. 270–75 c.e.).
ILLYRIAN EMPERORS (268–305 C.E.)
Th e Illyrian emperors were primarily army offi cers from the
Balkans. For most of their reign they tended to be murdered
by their troops and replaced by another offi cer. Th e fi rst Il-
lyrian emperor was Claudius II (r. 268–70 c.e.), who was also
called Gothicus. He defeated the Goths and drove them back
beyond the Danube. His successor, Aurelian, recovered the
lost territories in the east and reclaimed Gaul. Eventually Ca-
rus (r. 282–83 c.e.) invaded the Parthian Empire, and again
the Romans sacked the Parthian capital, Ctesiphon.
Th e most important of the Illyrian emperors was Diocle-
tian (r. 284–305 c.e.). He established elaborate royal ceremo-
nies that kept him remote from the general populace, perhaps
to lessen the opportunity for assassination. To make the Ro-
man Empire more secure internally, he separated the military
from the civil authority in the provinces, making it harder for a
governor to declare himself independent of Rome. Further, he
broke Rome’s provinces into many smaller provinces to make
sure no single province could become powerful enough to
challenge the central government. To make the Roman Empire
more secure externally, he increased Rome’s standing army by
about 100,000 troops to more than 400,000. In addition, he
made sure soldiers were paid well, in full, and on time.
THE TETRARCHY (284–337 C.E.)
In 285 c.e. Diocletian decided to share power because he was
overwhelmed by all the work that needed to be done to pre-
serve the Roman Empire. Th at year he appointed Maximian
(r. 286–305 c.e.) to be a junior emperor, but in 286 c.e. he
made Maximian a senior emperor, placing Maximian equal
to himself. When they added two junior emperors who had
separate responsibilities for the eastern and western parts of
the empire, their government became a tetrarchy, meaning
four rulers.
In 305 c.e. Diocletian and Maximus chose to retire, leav-
ing governance to their junior emperors, who then became
senior emperors. One of them was Constantius I (r. 305–6
c.e.). He had been in charge of the Western Roman Empire,
and when he died the western provinces expected his son
Constantine I (r. 306–37 c.e.) to become emperor. In 306 c.e.
Maxentius (r. 306–12 c.e.), the son of Maximian, declared
himself emperor. Th is resulted in a series of civil wars that
ended the Tetrarchy and concluded in 324 c.e. with Constan-
tine I as sole emperor.
HOUSE OF CONSTANTINE (306–364 C.E.)
Constantine I became known as Constantine the Great. In
312 c.e. he invaded Italy and fought and defeated the army
of Maxentius at Augusta Taurinorum, modern-day Turin,
and Aquileia, modern-day Verona, but Maxentius was a
tough opponent with an army that was determined to win.
Before the climactic Battle of Milvian Bridge in central Italy,
Constantine I had a vision of the Christian cross and heard a
voice that said he would win if he carried the cross into battle,
which he did. Although he waited until he was on his death
bed to be baptized, he considered himself a Christian from
that time on. Th ousands of Christians had been slaughtered
as enemies of the state during the reign of Diocletian, making
Constantine’s conversion very dramatic.
He agreed to allow Licinius (r. 308–24 c.e.) to rule the
eastern empire, including Egypt, while he ruled the rest of
North Africa as well as the western empire. In 316 c.e. Con-
stantine I seized the Balkans and Greece, which had been un-
der Licinius’s rule. In 324 c.e. he advanced into Th race, where
he decisively defeated Licinius’s army at Adrianople, present-
day Edirne, and won the rest of the Roman Empire.
During his reign Constantine I strengthened the empire’s
army and defenses, especially along the Danube, where he
built defensive earthworks. He was deeply involved in Chris-
tian aff airs, even joining in theological meetings about the
future course of Christianity. He built churches in Jerusalem
at holy sites, such as the cave where Christ had been interred.
In 330 c.e. he moved the capital of the empire to Byzantium,
modern-day Istanbul, and renamed it Constantinople.
Constantine I left his empire to his sons, Constantine II
(r. 337–40 c.e.), Constans I (r. 337–50 c.e.), and Constantius
II (r. 337–61 c.e.), as well as to Flavius Iulius Dalmatius, the
son of his stepbrother. His sons murdered Dalmatius. Con-
stantine II was killed fi ghting Constans; Constans was killed
by the self-proclaimed emperor Magnentius (r. 350–53 c.e.);
Constantius II died of an illness. Th eir cousin Julian (r. 361–
63 c.e.) seized power. Before Julian challenged Constantius
II for the throne, he had distinguished himself with victo-
ries over Germanic tribes at the Rhine. Julian believed in the
traditional Roman gods and tried to suppress the Christian
faith. In 363 c.e. he invaded the Parthian Empire, but he was
killed in battle.HOUSE OF VALENTINIAN (364–395 C.E.)
In 364 c.e. the Roman Empire was divided into west and east.
Th e west was ruled by Valentinian I (r. 364–75 c.e.), and the
east was ruled by his brother Valens (r. 364–78 c.e.). In 357
c.e. the Germanic tribe the Visigoths fl ed the Huns into the
Balkans of the empire. In 378 c.e. Valens tried to drive the
Visigoths out of the empire, but he was killed and his army
defeated at Adrianople. In the west Valentinian I had been
succeeded by his son Gratian (r. 375–83 c.e.), who appointed
the general Th eodosius I (r. 379–95 c.e.) ruler of the eastern
empire. In 382 c.e. Th eodosius I and the Visigoths made a
peace treaty that allowed the Visigoths to settle in the Roman
Empire. From 394 to 395 c.e. Th eodosius I ruled both east
and west of the empire.HOUSE OF THEODOSIUS (379–565 C.E.)
Th e Visigoths tried invading Italy in 401 c.e., during the
reign of Th eodosius I’s son Honorius (r. 395–423 c.e.), butempires and dynasties: Rome 417