The Great Roman Emperor Theodosius I

Obelisk of Theodosius I against a blue sky
Obelisk of Theodosius I, originally erected by Tuthmosis III in front of the temple of Karnak (15th century BC), Istanbul, Turkey. De Agostini / Archivio J. Lange / Getty Images

Under Emperor Valentinian I (r. 364-375), army officer Flavius Theodosius was stripped of command and exiled to Cauca, Spain, where he had been born in about 346. Despite such inauspicious beginnings, Theodosius, with his 8-year-old son installed in name as ruler of the Western Empire, became the last emperor to rule the entire Roman Empire in fact.

Probably two to three years after Valentinian exiled Theodosius (and executed his father), Rome needed Theodosius again. The empire was a formidable power at this time. Thus it was against all odds that on August 9, 378 the Visigoths trounced the Eastern Empire and killed its emperor (Valens [r. A.D. 364-378]) at the momentous Battle of Adrianople. Although it took a while for the after-effects to play out, this defeat is a major event to look at when tracing the fall of the Roman Empire.

With the eastern emperor dead, his nephew, the western Emperor Gratian, needed to reclaim command of Constantinople and the rest of the eastern part of the empire. To do so he sent in his best general—the formerly-exiled Flavius Theodosius.


A.D. c. 346-395; (r. A.D. 379-395)
Place of Birth:

Cauca, in Hispania [see sec. Bd on Map]


Theodosius the Elder and Thermantia


  • Aelia Flavia Flaccilla;
  • Galla


  • Arcadius (made Augustus on 19 January 383), Honorius (made Augustus on 23 January 393), and Pulcheria;
  • Gratian and Galla Placidia
  • (by adoption) Serena, his niece

Claim to Fame:

The last ruler of the entire Roman Empire; effectively put an end to pagan practices.

Theodosius' Hazardous Rise to Power

Theodosius' own father had been a senior military officer in the Western Empire. Emperor Valentinian had honored him by appointing him magister equitum praesentalis 'Master of the Horse in the Presence of the Emperor' (Ammianus Marcellinus 28.3.9) in 368 and then executed him in early 375 for unclear reasons. Perhaps Theodosius' father was executed for trying to intercede on behalf of his son. At about the time Emperor Valentinian executed his father, Theodosius went into retirement in Spain.

It was only after Valentinian's death (November 17, 375) that Theodosius regained his commission. Theodosius obtained the rank of the magister militum per Illyricum 'Master of the Soldiers for the Prefecture of Illyricum' in 376, which he kept until January 379 when Emperor Gratian appointed him co-Augustus to replace Emperor Valens. Gratian may have been coerced into making the appointment.

Barbarian Recruits

The Goths and their allies were ravaging not only Thrace but also Macedonia and Dacia. It was the eastern emperor, Theodosius' job to suppress them while the western emperor, Gratian attended to matters in Gaul. Although Emperor Gratian provided the Eastern Empire with some troops, Emperor Theodosius needed more -- because of the devastation that had been caused by the Battle at Adrianople. So he recruited troops from among the barbarians. In an only partially successful attempt to stave off barbarian defection, Emperor Theodosius made a trade: he sent some of his new, questionable recruits to Egypt to be exchanged for presumed-loyal Roman soldiers. In 382 Emperor Theodosius and the Goths reached an agreement: Emperor Theodosius permitted the Visigoths to retain some autonomy while living in Thrace, and many of the Goths enlisted in the imperial army, and especially the cavalry, which had proved to be one of the Roman weaknesses at Adrianople.

The Emperors & Their Domains

From Julian to Theodosius & Sons. (Simplified)

NB: Valeo is the Latin verb 'to be strong'. It was a popular base for men's names in the Roman Empire. Valentinian was the name of 2 Roman emperors during the lifetime of Theodosius, and Valens was that of a third.



(West) (East)

Valentinian I / Gratian


Gratian / Valentinian II


Theodosius / Arcadius

Maximus Emperor

In January of 383, Emperor Theodosius named his young son Arcadius successor. Maximus, a general who had served with Theodosius' father and may have been a blood relative, may have hoped to be named, instead. That year Maximus' soldiers proclaimed him emperor. With these approving troops, Maximus entered Gaul to face Emperor Gratian. The latter was betrayed by his own troops and killed in Lyons by Maximus' Gothic magister equitum. Maximus was preparing to advance on Rome when Emperor Gratian's brother, Valentinian II, sent a force to meet him. Maximus agreed to accept Valentinian II as ruler of part of the Western Empire, in 384, but in 387 he advanced against him. This time Valentinian II fled to the East, to Emperor Theodosius. Theodosius took Valentinian II into protection. Then he led his army to fight against Maximus in Illyricum, at Emona, Siscia, and Poetovio [see map]. Despite many Gothic troops defecting to Maximus' side, Maximus was captured and executed at Aquileia on August 28, 388. (Valentinian II, Theodosius' brother-in-law through his second marriage, was killed or committed suicide in May of 392.) One of the defecting Gothic leaders was Alaric, who fought for Emperor Theodosius in 394 against Eugenius, another pretender to the throne -- which he lost in the civil war battle on the river Frigidus in September -- and then against Emperor Theodosius' son, but is best known for sacking Rome.


From the time of Emperor Jovian (377), there had been a Roman treaty with the Persians, but there were skirmishes along the borders. In 387, Emperor Theodosius' magister peditum praesentalis, Richomer, put an end to these. Conflict over Armenia picked up again, until another of Emperor Theodosius' officials, his magister militum per Orientem, Stilicho, arranged a settlement. Stilicho was to become a major figure in Roman history of the period. In an effort to tie Stilicho to his family and presumably strengthen the claim of Emperor Theodosius' son Arcadius, Emperor Theodosius married his niece and adoptive daughter to Stilicho. Emperor Theodosius appointed Stilicho regent over his younger son Honorius and possibly (as Stilicho claimed), over Arcadius, as well.

Theodosius on Religion

Emperor Theodosius had been tolerant of most pagan practices, but then in 391 he sanctioned the destruction of the Serapeum at Alexandria, enacted laws against pagan practices, and put an end to the Olympic games. He is also credited with putting an end to the power of the Arian and Manichean heresies in Constantinople while establishing Catholicism as the state religion.


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Your Citation
Gill, N.S. "The Great Roman Emperor Theodosius I." ThoughtCo, Apr. 5, 2023, Gill, N.S. (2023, April 5). The Great Roman Emperor Theodosius I. Retrieved from Gill, N.S. "The Great Roman Emperor Theodosius I." ThoughtCo. (accessed May 28, 2023).