Alexander divided his troops into three bodies. One division was to act towards the north, to take advantage of the friendly disposition of Chosroes, king of Armenia, and, traversing his strong mountain territory, to direct its attack upon Media, into which Armenia gave a ready entrance. Another was to take a southern line, and to threaten Persia Proper from the marshy tract about the junction of the Euphrates with the Tigris, a portion of the Babylonian territory. The third and main division, which was to be commanded by the emperor in person, was to act on a line intermediate between the other two, which would conduct it to the very heart of the enemy’s territory, and at the same time allow of its giving effective support to either of the two other divisions if they should need it. The plan of operations appears to have been judiciously constructed, and should perhaps be ascribed rather to the friends whom the youthful emperor consulted than to his own unassisted wisdom. But the best designed plans may be frustrated by unskilfulness or timidity in the execution; and it was here, if we may trust the author who alone gives us any detailed account of the campaign, that the weakness of Alexander’s character showed itself. The northern army successfully traversed Armenia, and, invading Media, proved itself in numerous small actions superior to the Persian force opposed to it, and was able to plunder and ravage the entire country at its pleasure. The southern division crossed Mesopotamia in safety, and threatened to invade Persia Proper. Had Alexander with the third and main division kept faith with the two secondary armies, had he marched briskly and combined his movements with theirs, the triumph of the Roman arms would have been assured. But, either from personal timidity or from an amiable regard for the anxieties of his mother Mamsea, he hung back while his right and left wings made their advance, and so allowed the enemy to concentrate their efforts on these two isolated bodies. The army in Media, favored by the rugged character of the country, was able to maintain its ground without much difficulty; but that which had advanced by the line of the Euphrates and Tigris, and which was still marching through the boundless plains of the great alluvium, found itself suddenly beset by a countless host, commanded by Artaxerxes in person, and, though it struggled gallantly, was overwhelmed and utterly destroyed by the arrows of the terrible Persian bowmen. Herodian says, no doubt with some exaggeration, that this was the greatest calamity which had ever befallen the Romans. It certainly cannot compare with Cannae, with the disaster of Varus, or even with the similar defeat of Crassus in a not very distant region. But it was (if rightly represented by Herodian) a terrible blow. It absolutely determined the campaign. A Caesar or a Trajan might have retrieved such a loss. An Alexander Severus was not likely even to make an attempt to do so.