Alexander pressed on to the northward and eastward in pursuit of Bessus, who had soon collected the scattered remains of his army, and was doing his utmost to get into a posture of defense. He did not, however, overtake him till he had crossed the Oxus, a large river which will be found upon the map, flowing to the northward and westward into the Caspian Sea. He had great difficulty in crossing this river, as it was too deep to be forded, and the banks and bottom were so sandy and yielding that he could not make the foundations of bridges stand. He accordingly made floats and rafts, which were supported by skins made buoyant by inflation, or by being stuffed with straw and hay. After getting his army, which had been in the mean time greatly re-enforced and strengthened, across this river, he moved on. The generals under Bessus, finding all hope of escape failing them, resolved on betraying him as he had betrayed his commander. They sent word to Alexander that if he would send forward a small force where they should indicate, they would give up Bessus to his hands. Alexander did so, intrusting the command to an officer named Ptolemy. Ptolemy found Bessus in a small walled town whither he had fled for refuge, and easily took him prisoner. He sent back word to Alexander that Bessus was at his disposal, and asked for orders. The answer was, "Put a rope around his neck and send him to me."