AMMIANUS, MARCELLINUS. - A pagan Latin historian of the 4th century, born at Antioch of a noble family. The year of his birth is not known, though it may be held to have occurred around 335; likewise we know nothing of his life until 353, when he was enrolled in the bodyguard of the protectores domestici, under the command of the master of the cavalry Ursicinus, whom A. was to follow faithfully until his dismissal. With Ursicinus in 353 he moved from Nisibis to Antioch, where the latter had been summoned by the Caesar Gallus to preside over the trial of the city's leading men; in 354 he moved on to Milan, where an order of the emperor Constantius had enjoined Ursicinus to present himself to answer the suspicions weighing upon him. He followed Ursicinus also into Gaul, where he had been sent to suppress the revolt of the usurper Silvanus, then again into the East when the Persians violated the frontiers of the Empire. A. took part in both these campaigns.
Interesting is his description of the campaign against the Persians (bks. XIX-XX), particularly of the siege of Amida, where he had taken refuge (359). Once the city was stormed, A. and Ursicinus escaped to Mytilene and then to Antioch, but the failure led to the dismissal of Ursicinus (360).
In 363 we find A. again in Persia, at the side of the emperor Julian, who on 26 July of that year gave up his life on the field. After the peace concluded by Jovian with the Persians, it seems that A. definitively abandoned arms and retired to private life, first at Antioch, then, after visiting various regions, among them Egypt and Greece, at Rome, where he devoted himself to the composition of his great historical work, in continuation of the Historiae of Tacitus. Whether in this last period of his life he exercised some civil magistracy remains a conjecture, while it is certain that the soldier was succeeded by the scholar. Libanius (Epist. 983) in 391 still recalls him at Rome, where he receives the applause of the people for the public reading of his Rerum gestarum libri. After that year there is no further record of him.
The complete Rerum gestarum libri were thirty-one, almost certainly all written before 400. Only the last eighteen have come down to us. The chronological limits of the narrative are indicated by A. in the conclusion of the work: « Haec ut miles quandam et graecus, a principatu Caesaris Nervae exorsus ad usque Valentis interitum pro virium explicavi mensura » (bk. XXXI), that is, from the reign of Nerva, with which the narrative of Tacitus stops, down to the death of Valens (96-378).
The first thirteen lost books, together with the preserved part of the fourteenth, carried the narrative down to the death of the Caesar Gallus (354), rather succinctly, as being less known to A., compiled for the most part from pre-existing documents. Books XV-XXV contain the events that occurred from the appointment of Julian as Caesar down to the death of Jovian (354-64). The remaining ones are devoted to the events that followed from the appointment of Valentinian down to the death of his brother Valens (364-78). The complete narrative of the surviving books is for the most part the fruit of the author's own experience.
Among all the pagan historiographers A. is certainly the only one who treats Christianity at length, and his testimony is precious for the history of the Church, because it is contemporary with the events narrated, worthy of belief for the purpose he pursued of telling the truth, and of greater value because the author is not a Christian. The assertion of C. Chifflet that A. was a Christian has no foundation, and his paganism is proved by his entire work. A.'s religion, however, was not that of the ancient Greeks and Romans; he did not believe in the gods of Olympus, whose existence he denies, but he believes in a God who is not a person, but a force that governs all things. In his religious conception he comes very close to the Neoplatonists, from whom he drew the religious freedom that permits each person to follow his own conscience. He had in fact a benevolent tolerance toward all religions, nor did he combat Christianity, as the other pagan writers had done; he appreciates on the contrary the Christian doctrines and professes admiration for the heroism of the martyrs, going so far as to censure the zeal of his hero Julian.
The Christian historians of antiquity and of the Middle Ages, with due exceptions, generally ignored A. and his work, only because he was a pagan, whereas he deserves a distinguished place among the sources for the history of the early Church, of which he remains an impartial witness.
The surviving manuscripts of A.'s work are no older than the 9th or 10th century. The editio princeps appeared in Rome in 1474 and is due to A. Sabino. Among the later editions those of E. de Valois (Paris 1636) and the other of J. A. Wagner (Leipzig 1808) deserve to be remembered for their valuable commentaries. The most recent edition is that of C. Clark (2 vols., Berlin 1910-15).