Also during this time, Alexander began to demand that his subjects treat him as a god. He thought of himself as their deliverer, as their savior from the cruelty of Darius and the Persian emperors and kings before him. He also thought of himself as more than just a man. In his own mind, he was invincible, a genius on the battlefield and in political matters. He foresaw a time when he would be the master of the known world. His thoughts full of such grandeur, he styled himself a god and demanded obedience from his new people.
Alexander and his men stayed through the winter before moving on, leaving local leaders in charge of Persepolis, with the promise that Alexander would be back to accept the throne of the empire. Then, he and his men went in search of Darius (who was, technically, still the emperor). By this time, Darius had become convinced that he couldn't defeat Alexander and had reduced himself to fleeing the countryside. His military commanders, none too pleased with this change of events, seized control of the situation and eventually seized control of Darius himself. His own viceroy, Bessus, took charge of Darius and kept him as a prisoner. The main Persian army was camped to the north, near the Caspian Sea. Alexander followed, of course.
When the two armies were within in sight of each other, the result didn't change. Bessus, not at all sure that he wanted to fight, led his men in a further retreat, further north, fading into the countryside. They left Darius behind, dead of stab wounds. When Alexander discovered the dead emperor, he had him sent back to Persepolis and buried with full royal honors. The quarry, however, was still to the north.
Alexander led his men across the region of Bactria and into the fabled mountains known as Paropanisus. (We call this the Hindu Kush today.) Along the way, some of Alexander's men, thinking that they would never see their homes again and convinced that their leader was going mad, began to plot against him. A great many of the men were still loyal to Alexander, however, and the plot was soon discovered. It was in a place called Drangiana that the first hints of Alexander's madness surfaced.
Philotas, the son of Parmenio, one of Alexander's most trusted and successful commanders, was suspected of being involved in the plot against Alexander. Philotas and his father were two of the king's dearest friends and had served with him from the beginning. However, Alexander must survive and teach a lesson to anyone wishing to oppose him. In a fit of calculated rage, Alexander ordered Philotas executed. Not content with that, however, he also ordered Parmenio killed, figuring that his loyalty would be in question from that point forward.
Alexander and his men caught up with Bessus, the runaway rebel, eventually. The result wasn't much of a battle, since the Persian forces were thinned from defeats and exhaustion. Bessus was captured and then cruelly tortured before being killed.
Alexander was master of the Persian Empire, but was he master of himself? He had become increasingly erratic and impulsive, even moreso than he had ever had been. These qualities had served him well on the battlefield, where he could use his "sixth sense" to discover where to penetrate the enemy's defenses; but the same qualities weren't working so well in the administration of an occupied territory. When Parmenio's cavalry refused to follow the army east, Alexander ordered them to go home (which is probably what they were ready for at that point anyway).
Impatient and still seeking some elusive goal, Alexander ordered his men to march ever eastward, in search of they knew not what. If Alexander had a goal in mind, he didn't readily share it with his troops. Eastward and northward hey moved, defeating armies as they went, over hundreds of miles of unfamiliar terrain, past the ancient trading post of Samarkand, and on into the heart of Asia.