Theodosius and the Roman Empire: Christianity and the 395 Division
Theodosius I ruled from 379 to 395 CE and briefly controlled both halves of the Roman Empire. His religious laws, civil wars and sons' succession.
Last updated October 2026
Contents11
- Theodosius and the Roman Empire: at a glance
- An empire shaken by Adrianople
- The Gothic settlement of 382
- Christianity as the state's favoured faith
- Laws against traditional worship
- Thessalonica, massacre and penance
- Civil wars and the last united rule
- Timeline of Theodosius I
- What the division of 395 meant
- Theodosius I and Theodosius II
- Verdict: Theodosius and the Roman Empire
Theodosius I ruled from 379 to 395 CE. He was the last emperor to control both halves of the Roman Empire. After his death, his sons Arcadius and Honorius headed separate courts, a division that became lasting. De Imperatoribus Romanis: Theodosius I
He also strengthened Nicene Christianity's official place. That change took laws, church choices and years of conflict. It did not turn every subject into a Christian at once. The Eastern Roman Empire overview explains the state that continued under Arcadius.
TL;DR: Theodosius became eastern emperor after the defeat at Adrianople. He settled with the Goths and fought two civil wars in the West. His laws favoured Nicene Christianity and restricted traditional worship. A massacre at Thessalonica led to public penance. He briefly ruled the whole empire, then died. His sons' separate courts continued the Roman state in different directions.
Theodosius and the Roman Empire: at a glance
The entries follow De Imperatoribus Romanis, Internet History Sourcebooks: Medieval Sourcebook.
| Field | Record | Status |
|---|---|---|
| Emperor | Theodosius I, called the Great | Reviewed |
| Eastern reign | 379-395 CE | Reviewed |
| Control of both halves | 394-395 CE | Reviewed |
| Religious policy | Official support for Nicene Christianity | Reviewed |
| Major civil-war opponents | Magnus Maximus and Eugenius | Reviewed |
| Death | 17 January 395 CE | Reviewed |
| Successors | Arcadius in the East, Honorius in the West | Reviewed |
| Theodosius II | His grandson, a different eastern emperor | Reviewed |
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An empire shaken by Adrianople
The eastern emperor Valens died at Adrianople in 378, and the eastern field army suffered a severe defeat. Gratian, the western emperor, chose Theodosius as his new colleague in 379. The new ruler had to rebuild forces and contain Gothic groups already inside Roman land. De Imperatoribus Romanis
Theodosius was an experienced military officer from a Spanish family. His father had also held high command. This gave him a place in the governing elite, though accounts of his early career contain uncertain points. His accession answered an urgent crisis, rather than a peaceful family handover.
The size of the state helped explain the need for another emperor. One court could not easily manage every frontier and army. Shared rule was already a known Roman solution. The later division of 395 did not invent the idea from nothing.
The Gothic settlement of 382
Theodosius fought the Goths but also made use of some groups as soldiers. In 382 he reached a settlement with those still resisting. They were allowed to settle in Roman land and supplied troops. The exact terms have not survived as a complete agreement. De Imperatoribus Romanis
That gap matters. This was not a modern treaty. Its exact terms and rights are harder to pin down. Historians instead have to reconstruct it from later events and reports.
Some autonomy is clear. Not every detail is clear.
The agreement eased an immediate military problem. It did not ensure that all Gothic forces would remain loyal to the emperor's heirs. Theodosius could win service from leaders in one campaign without settling their relationship with the state for all time.
Christianity as the state's favoured faith
The Edict of Thessalonica set an approved Christian faith. It followed the bishops of Rome and Alexandria. It backed the belief now called Nicene Christianity, including the shared divine status of Father, Son and Holy Spirit. The translated text is in Internet History Sourcebooks: Medieval Sourcebook.
This was more specific than simply favouring Christians over non-Christians. Christian groups disagreed about doctrine. Theodosius backed one side, removed rival bishops from churches and called a council at Constantinople in 381. Policy on faith could also divide Christians as well as separate them from others. De Imperatoribus Romanis
The phrase “Christianity became the state religion” is a useful short answer. It should not imply that Constantine had done nothing before him or that later rulers had nothing left to do. Theodosius strengthened an existing Christian court through legal and institutional choices.
Laws against traditional worship
Theodosius issued restrictions on traditional forms of worship, especially late in his reign. Laws against sacrifice, visits to sanctuaries and honours to divine images made the old public cults harder to keep. They helped change the state's formal relationship with religion. De Imperatoribus Romanis
Enforcement was uneven. A law shows what the government wanted. It does not prove that every local custom ended at once. Officials, bishops and monks had their own aims, and local conflicts shaped what happened.
The destruction of the Serapeum in Alexandria is a clear case of that tension. The emperor sanctioned action after a local crisis. The episode joined imperial power to pressure from local Christian actors. It should not be made into a claim that he personally ordered every temple destroyed.
Thessalonica, massacre and penance
In 390, imperial troops massacred people at Thessalonica after unrest and the killing of a senior commander. Ambrose, bishop of Milan, challenged Theodosius over the act. The emperor performed public penance. De Imperatoribus Romanis
The event became an important story about a bishop confronting imperial power. Its basic sequence is clearer than every later scene told about it. The texts give death counts that cannot be checked. No full list of victims survives to test them.
Penance did not make the bishop the emperor's ruler in all affairs. It did show that standing in the Church could impose a public cost on an emperor. The relationship between church and court was close. But neither acted as a single, simple body.
Civil wars and the last united rule
Theodosius fought Magnus Maximus in 388 and later Eugenius in 394. Both conflicts concerned control of the western government. The second ended with victory at the Frigidus. Theodosius then controlled both halves of the empire for a short period. De Imperatoribus Romanis
Later Christian accounts gave the Frigidus a strongly sacred meaning. It was also a contest between rival political coalitions. Eugenius himself was Christian.
The sides did not divide neatly into Christian and pagan armies. Both had mixed motives.
The wars used troops that were also needed on the frontiers. Winning the whole state had a military cost. A final period of unity was therefore not the same as a long, settled recovery.
Timeline of Theodosius I
The entries follow De Imperatoribus Romanis.
| Date | Event | Result |
|---|---|---|
| 378 CE | Valens dies at Adrianople | An eastern military crisis |
| 379 | Theodosius becomes eastern emperor | Army rebuilding begins |
| 381 | Council at Constantinople | Nicene church policy gains support |
| 382 | Settlement with the Goths | Some groups settle and serve in the army |
| 388 | Magnus Maximus defeated | Western affairs come under his influence |
| 390 | Thessalonica massacre and penance | Ambrose challenges imperial conduct |
| 394 | Eugenius defeated at the Frigidus | Brief rule over both halves |
| 395 | Theodosius dies | Arcadius and Honorius lead separate courts |
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What the division of 395 meant
Arcadius ruled in the East and Honorius in the West. Both had already received imperial rank. Their succession followed their father's dynastic plans, rather than a decision to end Rome and create two unrelated countries. De Imperatoribus Romanis
The courts developed different political and military paths. The eastern state proved more durable. The Western Roman Empire later lost land and its resident imperial office. The East continued as the state now called Byzantine.
For an earlier emperor with a very different religious programme, see Julian. For the start of the imperial system, see was Julius Caesar an emperor.
Theodosius I and Theodosius II
Theodosius II was the first ruler's grandson, not another name for him. He ruled the eastern empire after Arcadius and died in 450. His name is linked to the later law collection called the Theodosian Code. De Imperatoribus Romanis
That collection includes laws from earlier emperors. The code collected laws from several rulers. Its name does not identify the author of every law. Keeping the two men separate avoids confusion between a religious edict and the later book that preserved it.
Verdict: Theodosius and the Roman Empire
Theodosius I strengthened Nicene Christianity and briefly brought the Roman Empire under one ruler. His civil wars, Gothic settlement and family succession had long effects. The division after his death was a change in courts, not an instant end to Roman identity. An account of his religious policy also needs both the laws and the limits of their enforcement. De Imperatoribus Romanis
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Questions people also ask
When did Theodosius I rule?
He was eastern emperor from 379 to 395 CE. After defeating Eugenius, he controlled both halves in 394-395. That brief final phase makes him the last emperor to rule the whole Roman Empire.
Did Theodosius make Christianity the state religion?
He made Nicene Christianity the approved form of faith and backed it with law and church policy. Earlier emperors had already favoured Christianity. His reign strengthened that position and restricted competing worship.
Why did the Roman Empire split in 395?
His sons Arcadius and Honorius headed separate eastern and western courts after his death. Shared rule had earlier precedents. The lasting separation developed from dynastic succession and the different needs of each court.
What happened at Thessalonica?
Imperial troops carried out a massacre after unrest in 390. Ambrose of Milan challenged Theodosius, who performed penance. Exact totals and some dramatic details in later stories are less secure.
Were Theodosius I and II the same person?
No. Theodosius II was his grandson and an eastern emperor who died in 450. The later Theodosian Code was compiled under him and preserved laws from several earlier rulers.
Who succeeded Theodosius I?
Arcadius in the East and Honorius in the West. Both were his sons and already held imperial rank. Their courts continued to govern parts of the same Roman political tradition.