Res Gestae

Their armies were led to the plain of Cibalae.[*](Cf. Amm. xxx. 7, 2.) Licinius had 35,000 infantry and cavalry; Constantine commanded 20,000. After an indecisive contest, in which 20,000 of Licinius’ foot soldiers and a part of his mail-clad horsemen were slain, he himself with a great part of his other cavalry made his escape under cover of night to Sirmium.

From there, taking with him his wife, his son, and his treasures, he went to Dacia and appointed Valens, who was commander on the frontier, to the rank of Caesar. Then, having through Valens mustered a large force at Hadrianopolis, a city of Thrace, he sent envoys to Constantine, who had established himself at Philippi, to treat for peace. When the envoys were sent back without accomplishing anything, the war was renewed and the two rivals joined battle on the plain of Mardia. After a long and indecisive struggle, the troops of Licinius gave way and night aided them to escape.