The force entrusted to Surenas comprised troops of both these classes. No estimate is given us of their number, but it was probably considerable. At any rate it was sufficient to induce him to make a movement in advance--to cross the Sinjar range and the river Khabour, and take up his position in the country between that stream and the Belik--instead of merely seeking to cover the capital. The presence of the traitor Abgarus in the camp of Crassus was now of the utmost importance to the Parthian commander. Abgarus, fully trusted, and at the head of a body of light horse, admirably adapted for outpost service, was allowed, upon his own request, to scour the country in front of the advancing Romans, and had thus the means of communicating freely with the Parthian chief. He kept Surenas informed of all the movements and intentions of Crassus, while at the same time he suggested to Crassus such a line of route as suited the views and designs of his adversary. Our chief authority for the details of the expedition tells us that he led the Roman troops through an arid and trackless desert, across plains without tree, or shrub, or even grass, where the soil was composed of a light shifting sand, which the wind raised into a succession of hillocks that resembled the waves of an interminable sea. The soldiers, he says, fainted with the heat and with the drought, while the audacious Osrhoene scoffed at their complaints and reproaches, asking them whether they expected to find the border-tract between Arabia and Assyria a country of cool streams and shady groves, of baths, and hostelries, like their own delicious Campania. But our knowledge of the geographical character of the region through which the march lay makes it impossible for us to accept this account as true. The country between the Euphrates and the Belik, as already observed, is one of alternate hill and plain, neither destitute of trees nor ill-provided with water. The march through it could have presented no great difficulties. All that Abgarus could do to serve the Parthian cause was, first, to induce Crassus to trust himself to the open country, without clinging either to a river or to the mountains, and, secondly, to bring him, after a hasty march, and in the full heat of the day, into the presence of the enemy. Both these things he contrived to effect, and Surenas was, no doubt, so far beholden to him. But the notion that he enticed the Roman army into a trackless desert, and gave it over, when it was perishing through weariness, hunger, and thirst, into the hands of its enraged enemy, is in contradiction with the topographical facts, and is not even maintained consistently by the classical writers.