Goth prisoners in a triumphal procession of Emperor Theodosius. Theodosius I (Latin: Flavius Theodosius Augustus;( 347  395), also known as Theodosius the Great, was Roman Emperor from AD 379 to AD 395. Theodosius was the last emperor to rule over both the eastern and the western halves of the Roman Empire. On accepting his elevation, he campaigned against Goths and other barbarians who had invaded the Empire;he failed to kill, expel, or entirely subjugate them, and after the Gothic War they established a homeland south of the Danube, in Illyricum, within the empire's borders.