Bessus, accompanied by the Persians who had taken part with him in the seizure of Darius, and by 7,000 of the Bactrians themselves and the Daans who dwelt on this side the Tanais,[498] was laying waste the country at the foot of Mount Caucasus, in order to prevent Alexander from marching any further, both by the desolation of the land between the enemy and himself and by the lack of provisions. But none the less did Alexander keep up the march, though with difficulty, both on account of the deep snow and from the want of necessaries; but yet he persevered in his journey. When Bessus was informed that Alexander was now not far off, he crossed the river Oxus,[499] and having burnt the boats upon which he had crossed, he withdrew to Nautaca[500] in the land of Sogdiana. He was followed by Spitamenes and Oxyartes, with the cavalry from Sogdiana, as well as by the Daans from the Tanais. But the Bactrian cavalry, perceiving that Bessus had resolved to take to flight, all dispersed in various directions to their own abodes. CHAPTER XXIX. CONQUEST OF BACTRIA, AND PURSUIT OF BESSUS ACROSS THE OXUS. Alexander now arrived at Drapsaca, and having there given his army a rest, he marched to Aornus and Bactra, which are the largest cities in the land of the Bactrians. These he took at the first assault; and left a garrison in the citadel of Aornus, over which he placed Archelaüs son of Androcles, one of the Companions. He appointed Artabazus the Persian, viceroy over the rest of the Bactrians, who were easily reduced to submission. Then he marched towards the river Oxus, which flows from mount Caucasus, and is the largest of all the rivers in Asia which Alexander and his army reached, except the Indian rivers; but the Indian rivers are the largest in the world. The Oxus discharges its water into the great sea which is near Hyrcania. When he attempted to cross the river it appeared altogether impassable; for its breadth was about six stades, and its depth was much greater than the proportion of its breadth. The bed of the river was sandy, and the stream so rapid, that stakes fixed deep into the bottom were easily rooted up from the earth by the mere force of the current, inasmuch as they could not be securely fixed in the sand. Besides this, there was a scarcity of timber in the locality, and he thought it would take a long time and cause great delay, if they brought from a distance the materials needful for making a bridge over the river. Therefore he collected the skins which the soldiers used for tent-coverings, and ordered them to be filled with chaff as dry as possible, and tied and stitched tightly together, so that the water might not penetrate into them.[501] When these were filled and stitched together, they were sufficient to convey the army across in five days. But before he crossed the river, he selected the oldest of the Macedonians, who were now unfit for military service, and such of the Thessalians as had volunteered to remain in