C.VibiusTrebonianusGallus, whose origin and early history are altogether unknown, held a high command in the army which marched to oppose the first great inroad of the Goths (A. D. 251), and, according to Zosimus, contributed by his treachery to the disastrous issue of the battle, which proved fatal to Decius and Herennius. [DECIUS ; HERENNIUS ETRUSCUS.] The empire being thus suddenly left without a ruler, Gallus was selected, towards the end of November, A. D. 251, by both the senate and the soldiers, as the person best qualified to mount the vacant throne, and Hostilianus, the surviving son of the late prince, was nominated his colleague. The first care of the new ruler was to conclude a peace with the victorious barbarians in terms of which they agreed to retire beyond the frontier, on condition of retaining their plunder and their captives and of receiving a fixed annual tribute as the price of future forbearance. The disgrace inflicted on the Roman name by this shameful concession excited the indignation of the whole nation, while the suicidal folly of the humiliating compact was soon manifested. For scarcely had the provinces enjoyed one short year of tranquillity, when fresh hordes from the north and east, tempted by the golden harvest which their brethren had reaped, poured down upon the Illyrian border. They were, however, driven back with great loss by Aemilianus, general of the legions in Moesia, whose triumphant troops forthwith proclaimed him Augustus. Gallus, upon receiving intelligence of this unexpected peril, despatched Valerianus [VALERIANUS] to quell the rebellion; but while the latter was employed in collecting an army from Germany and Gaul, Aemilianus, pressing forwards, had already entered Italy. Compelled by the urgency of the danger, Gallus, accompanied by Volusianus [VOLUSIANUS], whom he had previously invested with all the imperial dignities, marched forth to meet his rival, but before any collision had taken place between the opposing armies, both father and son were slain by their own soldiers, who despaired of success under such leaders. The precise date of this event has given rise to controversy among chronologers, some of whom fix upon the year 253, and others upon that of 254.
The name of Gallus is associated with nothing but cowardice and dishonour. The hatred and contempt attached to his memory may have led to the reports chronicled by Zosimus and Zonaras that the defeat of Decius was caused by his perfidy, and that he subsequently became the murderer of Hostilianus [HOSTILIANUS]. In addition to the misery produced by the inroads of the barbarians during this reign, great dismay arose from the rapid progress of a deadly pestilence which, commencing in Ethiopia, spread over every region of the empire, and continued its ravages for the space of fifteen years. (Zonar. 12.20, 21; Zosim. 1.23-28; Victor, de Caes. 30, Epit. 30; Eutrop. 9.5; Jornandes, de Reb. Goth. 19.)
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