GRATIAN (FLAVIUs GRATIANUS AUGUSTUS), Roman em peror 375-383, son of Valentinian I. by Severa, was born at Sirmium in Pannonia, on April 18 or May 23, 359. On Aug. 24, 367, he received from his father the title of Augustus. On the death of Valentinian (Nov. 17, 375) the troops in Pannonia pro claimed his infant son (by a second wife Justina) emperor under the title of Valentinian II. (q.v.). Gratian acquiesced in their choice; reserving for himself the administration of the Gallic provinces, he handed over Italy, Illyria and Africa to Valentinian and his mother, who fixed their residence at Milan. The division, however, was merely nominal, and the real authority remained in the hands of Gratian. The eastern portion of the empire was under the rule of his uncle Valens. In May 378 Gratian com pletely defeated the Lentienses, the southernmost branch of the Alamanni, at Argentaria, near the site of the modern Colmar.
When Valens met his death fighting against the Goths near Adrianople on Aug. 9 in the same year, the government of . the eastern empire devolved upon Gratian, but feeling himself unable to resist unaided the incursions of the barbarians, he ceded it to Theodosius (Jan. 379). With Theodosius he cleared the Balkans of barbarians. Gratian governed at first with energy and success, but gradually he sank into indolence, occupied himself chiefly with hunting, and became a tool in the hands of the Frankish general Merobaudes and bishop Ambrose. By taking into his personal service a body of Alani, and appearing in public in the dress of a Scythian warrior, he aroused the contempt and resent ment of his Roman troops. A Roman named Maximus raised the standard of revolt in Britain, and invaded Gaul with a large army, upon which Gratian, who was then in Paris, being deserted by his troops, fled to Lyons, where, through the treachery of the governor, he was delivered over to one of the rebel generals and assassinated on Aug. During the reign of Gratian orthodox Christianity for the first time became dominant throughout the empire. In dealing with pagans and heretics Gratian, who during his later years was greatly influenced by Ambrose, bishop of Milan, exhibited severity and injustice at variance with his usual character. He prohibited heathen worship at Rome ; refused to wear the insignia of the pontifex maximus as unbefitting a Christian; removed the altar of Victory from the senate-house at Rome, in spite of the re monstrance of the pagan members of the senate, and confiscated its revenues ; forbade legacies of real property to the Vestals; and abolished other privileges belonging to them and to the pontiffs.
For Gratian's treatment of the heretics the church histories of the period should be consulted.
See Ammianus Marcellinus xxvii.—xxxi. ; Aurelius Victor, Epit. 47; Zosimus iv. vi.; Ausonius (Gratian's tutor) especially the Gratiarum actio pro consulate; Symmachus x. epp. 2 and 61; Ambrose, De fide, prolegomena to Epistolae II, 17, 21 Consolatio de obitu Valentiniani; H. Richter, Das westromische Reich, besonders unter den Kaisern Gratian, Valentinian II. and Maximus (i865) ; A. de Broglie, L'Eglise et l'empire romain au IVe siecle (4th ed., 1882) ; H. Schiller, Geschichte der romischen Kaiserzeit (1883-86) , iii., iv. 31-33 ; Gibbon, Decline and Fall, ch. 27 ; R. Gumpoltsberger, Kaiser Gratian (1879) ; T. Hodgkin, Italy and her Invaders (1892), vol. i.; J. Wordsworth in Smith's Dictionary of Christian Biography.