Zosimus, New History 2.18
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.
[2.18.1] The empire being thus devolved on Constantine and Licinius, they soon quarrelled. Not because Licinius gave any cause for it, but that Constantine, in his usual manner, was unfaithful to his agreement, by endeavoring to alienate from Licinius some nations that belonged to his dominions. By this means an open rupture ensued, and both prepared for war.
[2.18.2] Licinius took up his head-quarters at Cibalis, a city of Pannonia, which stands on a hill. The road to which is rugged and narrow. The greatest part of this road is through a deep morass, and the remainder up a mountain, on which stands the city. Below it extends a spacious plain, which entertains the view with a boundless prospect. On this Licinius fixed his camp, and extended the body of his army under the hill, that his flanks might be protected from the enemy.
[2.18.3] Constantine in the meantime drew up his men near the mountain, placing the horse in front, thinking that to be the best disposition lest the enemy should fall upon the foot, who moved but slowly, and hinder their advance. Having done this, he immediately gave the charge, and attacked the enemy.
[2.18.4] This engagement was one of the most furious that was ever fought; for when each side had expended their darts, they fought a long time with spears and javelins; and after the action had continued from morning to night, the right wing, where Constantine himself commanded, began to prevail. The enemy being routed, Licinius's troops, seeing him mounted and ready to fly, dared not stay to eat their portions, but left behind them all their cattle and provisions, taking only as much food as would suffice for one night, and marched with great precipitation along with Licinius to Sirmium.
[2.18.5] Sirmium is a city of Pannonia, by which runs the river Saus, which discharges itself into the Ister. In passing this town he broke down the bridge over the river, and marched on with an intention to levy troops in Thrace.