Zosimus, New History 1.23

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 ZosimusNew 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.

[1.23.1] The Scythians, taking advantage of the disorder which every where prevailed through the negligence of Philip, crossed the Tanais, and pillaged the countries in the vicinity of Thrace. But Decius, marching against them, was not only victorious in every battle, but recovered the spoils they had taken, and endeavoured to cut off their retreat to their own country, intending to destroy them all, to prevent their ever again, making a similar incursion. 

[1.23.2] For this purpose he posted Gallus on the bank of the Tanais with a competent force, and led in person the remainder of his army against the enemy. This expedition exceeded to his utmost wish; but Gallus, who was disposed to innovation, sent agents to the barbarians, requesting their concurrence in a conspiracy against Decius. To this they gave a willing assent, and Gallus retained his post on the bank of the Tanais, but the barbarians divided themselves into three battalions, the first of which posted itself behind a marsh. 

[1.23.3] Decius having destroyed a considerable number of the first battalion, the second advanced, which he likewise defeated, and discovered part of the third, which lay near the marsh. Gallus sent intelligence to him, that he might march against them across the fen. Proceeding therefore incautiously in an unknown place, he and his army became entangled in the mire, and under that disadvantage were so assailed by the missiles of the barbarians, that not one of them escaped with life. Thus ended the life of the excellent emperor Decius.