Zosimus, New History 4.38
Zosimus (Greek Ζώσιμος): Early Byzantine, pagan author of a history of the Roman Empire, published in the first quarter of the sixth century CE.
The translation of Zosimus' New History offered here was printed in 1814 by W. Green and T. Chaplin in London, and was probably prepared by J. Davis of the Military Chronicle and Military Classics Office. The translator is anonymous. The text was found at Tertullian.org. The notes were added by Jona Lendering.
[4.38.1] As to the calamities which the Roman empire suffered from that period, a distinct account of the facts themselves will be the best demonstration. About this time, a nation of Scythia made its appearance from beyond the Ister, who were never before known to the inhabitants of those countries. They are called, by the barbarians in those parts, the Greuthinges. These being very numerous, furnished with arms of every description, and remarkably robust, easily overpowered the barbarians of the interior, proceeded as far as the banks of the Ister, and demanded permission to cross that river.
[4.38.2] Promotus, the commander of the forces in that quarter, drew out his troops as far as he could extend them along the bank of the river, and hindered the passage of the barbarians. While he was thus employed, he invented a stratagem to this effect. He called to him some of his own soldiers, who understood their language, and in whom he could confide in affairs of that nature, and sent them to agree with the barbarians upon betraying their own party.
[4.38.3] These men proposed to the barbarians to deliver the whole army into their hands in consideration of a large reward. The barbarians replied, that they were not able to give so much. However, to induce them to believe their promises, they adhered to their original proposals, and would not abate in any part of the reward.
[4.38.4] At length they agreed to the sum, which was in part to be paid immediately, and the remainder at the accomplishment of the treason. Having arranged the method of giving the signal, and the time for the execution of the project, they communicated to the commander each circumstance, that the barbarians would commence the enterprize in the night, and would cross the river to attack the Roman army.
[4.38.5] The barbarians, therefore, having placed all their best troops on board a great number of small vessels, commanded them to cross over first, and to fall on the soldiers while they were asleep. Next to these, they sent those of an inferior description to support the former when they had commenced the attack, and after them the useless multitude of every age, who are ready to boast of victories which others have gained.