It is uncertain what choice the proconsul would have made, had the decision been left simply to his own judgment.  Probably the Romans had a most dim and indistinct conception of the geographical character of the Mesopotamian region, and were ignorant of its great difficulties.  They remained also, it must be remembered, up to this time, absolutely unacquainted with the Parthian tactics and accustomed as they were to triumph over every enemy against whom they fought, it would scarcely occur to them that in an open field they could suffer defeat.  They were ready, like Alexander, to encounter any number of Asiatics, and only asked to be led against the foe as quickly as possible.  When, therefore, Abgarus, the Osrhoene prince, soon after Crassus had crossed the Euphrates, rode into his camp, and declared that the Parthians did not intend to make a stand, but were quitting Mesopotamia and flying with their treasure to the remote regions of Hyrcania and Scythia, leaving only a rear guard under a couple of generals to cover the retreat, it is not surprising that the resolution was taken to give up the circuitous route of the Euphrates, and to march directly across Mesopotamia in the hope of crushing the covering detachment, and coming upon the flying multitude encumbered with baggage, which would furnish a rich spoil to the victors.  In after times it was said that C. Cassius Longinus and some other officers were opposed to this movement, add foresaw its danger; but it must be questioned whether the whole army did not readily obey its leader’s order, and commence without any forebodings its march through Upper Mesopotamia.  That region has not really the character which the apologists for Roman disaster in later times gave to it.  It is a region of swelling hills, and somewhat dry gravelly plains.  It possesses several streams and rivers, besides numerous springs.  At intervals of a few miles it was studded with cities and villages; nor did the desert really begin until the Khabour was crossed.  The army of Crassus had traversed it throughout its whole extent during the summer of the preceding year, and must have been well acquainted with both its advantages and drawbacks.  But it is time that we should consider what preparations the Parthian monarch had made against the threatened attack.  He had, as already stated, come to terms with his outlying vassals, the prince of Osrhoene, and the sheikh of the Scenite Arabs, and had engaged especially the services of the former against his assailant.  He had further, on considering the various possibilities of the campaign, come to the conclusion that it would be best to divide his forces, and, while himself attacking Artavasdes in the mountain fastnesses of his own country, to commit the task of meeting and coping with the Romans to a general of approved talents.  It was of the greatest importance to prevent the Armenians from effecting a junction with the Romans, and strengthening them in that arm in which they were especially deficient,