Ammianus Marcellinus Res Gestae 18.7.10

[10] Therefore, being unexpectedly disappointed in the hope that they had conceived, they turned to embrace whatever the chance of fortune should offer; and on holding a council, with reference to the sudden urgent difficulties of their present situation, Antoninus, on being bidden to say what he thought, began by advising that they should turn their march to the right, in order to make a long detour through regions abounding in all sorts of supplies, and still untouched by the Romans in the belief that the enemy would march straight ahead, ¹ and that they should go under his guidance to the two garrison camps of Barzalo and Claudias: for there the river was shallow and narrow near its source, and as yet increased by no tributaries, and hence was fordable and easy to cross.