A second force , under Avidius Cassius and the III Gallica , moved down the Euphrates , and fought a major battle at Dura . By the end of the year , Cassius ' army had reached the twin metropolises of Mesopotamia : Seleucia on the right bank of the Tigris and Ctesiphon on the left .
A second force , under Avidius Cassius and the III Gallica , moved down the Euphrates , and fought a major battle at Dura.p163 By the end of the year , Cassius ' army had reached the twin metropolises of Mesopotamia : Seleucia on the right bank of the Tigris and Ctesiphon on the left .