The numerous and flourishing Greek and half-Greek towns in the regions along the Euphrates and Tigris, above all the great city of Seleucia, were altogether averse to the Parthian rule; all the Greek townships with which the Romans came into contact had now, like the citizens of Carrhae at an earlier time,( 4) practically shown how ready they were to shake off the intolerable foreign yoke and to receive the Romans as deliverers, almost as countrymen.
The Arab prince Abgarus, who commanded the desert of Edessa and Carrhae and thereby the usual route from the Euphrates to the Tigris, had arrived in the camp of the Romans to assure them in person of his devotedness.

The Parthians had appeared to be wholly unprepared.
The Euphrates Crossed Accordingly (701) the Euphrates was crossed (near Biradjik).
To reach the Tigris from this point they had the choice of two routes; either the army might move downward along the Euphrates to the latitude of Seleucia where the Euphrates and Tigris are only a few miles distant from each other; or they might immediately after crossing take the shortest line to the Tigris right across the great Mesopotamian desert.

The former route led directly to the Parthian capital Ctesiphon, which lay opposite Seleucia on the other bank of the Tigris; several weighty voices were raised in favour of this route in the Roman council of war; in particular the quaestor Gaius Cassius pointed to the difficulties of the march in the desert, and to the suspicious reports arriving from the Roman garrisons on the left bank of the Euphrates as to the Parthian warlike preparations.

But in opposition to this the Arab prince Abgarus announced that the Parthians were employed in evacuating their western provinces.

They had already packed up their treasures and put themselves in motion to flee to the Hyrcanians and Scythians; only through a forced march by the shortest route was it at all possible still to reach them; but by such a march the Romans would probably succeed in overtaking and cutting up at least the rear-guard of the great army under Sillaces and the vizier, and obtaining enormous spoil.