Who Was Emperor Theodosius and Why Is He Important?

Flavius Theodosius, reigning from 379 to 395 AD, was a Roman emperor whose tenure included major military crises and religious changes that shaped the future of Europe. Born in Hispania, he ascended to power during a period of instability. He was the last emperor to govern the entirety of the Roman Empire before its final, permanent division between his two sons.

Theodosius’s Rise to Power

Flavius Theodosius was born in Hispania to a high-ranking military officer, Count Theodosius. He pursued a military career and secured his own command in Moesia in 374, achieving some success against the Sarmatians. His career took a downturn when he was forced into retirement on his family estates in Spain following his father’s execution under unclear circumstances.

Theodosius’s recall to service was a direct consequence of a military disaster for the Roman Empire. On August 9, 378, the Eastern Roman Emperor Valens was killed and his army was decimated by the Goths at the Battle of Adrianople. This defeat left the Balkans vulnerable to pillaging and created a power vacuum in the East that the Western Emperor Gratian could not manage alone.

Faced with a ravaged army and a shortage of commanders, Gratian turned to Theodosius. Gratian appointed Theodosius as his co-emperor with the rank of Augustus at Sirmium on January 19, 379. Theodosius was tasked with taking control of the Gothic crisis and stabilizing the Eastern provinces.

Major Military and Political Events

Upon his ascension, Theodosius confronted the Goths, who were established within Roman territory after their victory at Adrianople. The Eastern Roman army was severely depleted, making it impossible to drive the Goths out. After years of intermittent warfare and negotiations, a settlement was reached.

The treaty, concluded on October 3, 382, established the Goths as allies of the empire, known as foederati. They were granted lands in Moesia and Dacia, south of the Danube River, where they lived with autonomy under their own leaders. In exchange, they were obligated to provide military service to the Roman army as a national contingent rather than being integrated into existing units.

Theodosius’s reign was also marked by two civil wars against usurpers in the West. The first was against Magnus Maximus, a general who was proclaimed emperor in Britain in 383 and killed the Western Emperor Gratian. After Maximus invaded Italy in 387, Theodosius intervened, marching his army, which included many Gothic foederati, and defeated Maximus’s forces, leading to his capture and execution in August 388.

A second civil war erupted after the Western Emperor Valentinian II died in 392. The Frankish general Arbogast elevated a rhetorician named Eugenius to the throne. Theodosius refused to recognize Eugenius and marched west again in 394. The decisive confrontation occurred at the Battle of the Frigidus, where Theodosius, again relying on his Gothic allies, secured a victory. Eugenius was executed, and Arbogast took his own life, leaving Theodosius as the sole ruler of the entire Roman Empire.

Religious Policies and Reforms

Theodosius’s reign is significant for its religious legislation, which altered the spiritual landscape of the Roman Empire. A devout Nicene Christian, he took steps to establish his faith as the official state religion. This process began after a severe illness in Thessalonica, during which he was baptized by the local Nicene bishop.

On February 27, 380, Theodosius and his co-emperors issued the Edict of Thessalonica. This edict mandated that all subjects of the empire adhere to the Nicene Creed, the orthodox Trinitarian Christian faith. The law branded other Christian doctrines, such as Arianism, as “heretical” and authorized state power to punish nonconformists. In 381, Theodosius convened the First Council of Constantinople, which further solidified Nicene orthodoxy by reaffirming the creed and condemning various heresies.

Following the edict, Theodosius enacted the “Theodosian Decrees,” which progressively restricted and eventually outlawed traditional pagan practices. Between 389 and 392, these decrees became increasingly stringent.

• Visits to pagan temples were forbidden.
• Public funding for traditional cults was cut.
• Remaining pagan holidays were abolished.
• The eternal flame in the Temple of Vesta was extinguished and the Vestal Virgins were disbanded.
• The ancient Olympic Games were suppressed, with the last recorded celebration in 393.

A defining moment of his reign was his relationship with the Bishop of Milan, Ambrose. In 390, the military governor of Thessalonica was killed in a riot. In response, Theodosius ordered a retaliation, and his troops massacred thousands of citizens in the city’s circus. Ambrose refused to give the emperor communion until he performed public penance. After several months, Theodosius submitted, publicly asking for forgiveness in the Milan cathedral, an act that demonstrated the growing power of the church.

The Theodosian Dynasty and Division of the Empire

Theodosius focused on securing the future of his lineage by establishing the Theodosian dynasty. He appointed his sons as co-emperors, elevating his elder son, Arcadius, to Augustus in 383, and his younger son, Honorius, to the same rank in 393. Arcadius was designated to rule the Eastern portion of the empire, while Honorius was intended for the West.

Upon Theodosius’s death in Milan on January 17, 395, this arrangement was formalized. The empire was officially divided between his two sons: Arcadius took control of the East from Constantinople, while the ten-year-old Honorius became emperor of the West. The great prefecture of Illyricum was also split between them.

While the empire had been administered by multiple emperors before, this division proved to be permanent. The young emperors were influenced by powerful advisors, such as Stilicho in the West and Rufinus in the East, whose rivalries deepened the separation. This final split set the two halves of the empire on distinct political and cultural paths.

Historical Significance and Legacy

Theodosius I is often referred to as “the Great,” a title reflecting the impact of his reign. His legacy is centered on his actions regarding religion and the political structure of the empire. He is remembered as the emperor who cemented the dominance of Christianity within the Roman world, a process started by Constantine but fully realized under his rule. His edicts made Nicene Christianity the official state religion and his suppression of paganism reshaped the religious identity of Europe for centuries.

The formal split of the empire between his sons is seen by many historians as a contributing factor to the eventual decline of the Western Roman Empire in the following century, as the two halves often failed to cooperate against external threats. The Eastern Roman Empire, which Theodosius had stabilized, would endure for another thousand years as the Byzantine Empire. His reign marked a transition from the classical Roman world to the emerging Byzantine and medieval eras.