Theodosius I was the last emperor to rule the whole Roman Empire
After victory over a western usurper in September 394, Theodosius I held every Roman province, east and west. Within months he was dead, his two young sons divided the empire between separate courts, and no single emperor ever governed all of it again.
The future emperor came into the world on 11 January, most likely in 347, somewhere in Hispania, son of Theodosius the Elder, a senior cavalry general under Valentinian I, and Thermantia. Ancient writers liked to compare him with Trajan, another Spanish-born emperor, though he never returned to Iberia once crowned. He probably grew up following his father's campaigns and reportedly loved history as a guide to conduct. He first appears on his father's 368 to 369 expedition to Britain against the Great Conspiracy.
By 374 he commanded in Moesia Prima on the Danube and repelled a Sarmatian incursion that autumn. Then his father abruptly fell from favour and was executed, perhaps through the scheming of the official Maximinus, and Theodosius withdrew to his Spanish estates. When Maximinus was himself ousted around April 376 and later put to death, Emperor Gratian rehabilitated the family.
In 379, after the eastern emperor Valens died at Adrianople fighting the Goths, Gratian named Theodosius his colleague to handle the crisis. Lacking the troops to expel the invaders, he let the Goths settle south of the Danube in 382 as autonomous allies, a bargain that troubled later emperors. In 386 he agreed with the Sasanian Empire to split Armenia, securing a lasting peace, and married Galla, sister of Valentinian II. He enlarged the Forum Tauri in Constantinople into the biggest public square known from antiquity.
A firm opponent of Arianism, he summoned the First Council of Constantinople in 381, which fixed Nicene doctrine as orthodox. He left most pagan cults alone and appointed non-Christians to high office, yet did nothing to stop Christians demolishing temples such as the Serapeum of Alexandria. He marched west twice, against Magnus Maximus in 388 and Eugenius in 394. He died on 17 January 395, and Arcadius and Honorius took the eastern and western halves.
Source: Theodosius I
