Darius was determined that he would not repeat the mistakes of Issus. There, he had engaged Alexander in a narrow mountain valley, where he was unable to bring to bear his numerical superiority. This time, he chose his own ground.
Gaugamela is located in northern Iraq, on open plains. Here, Darius was able to deploy the full force of his 200,000 men. Alexander had only about 40,000. Darius was sure of victory.
His soldiers, however, were less sure. Alexander did not even try to out-flank such a superior force. Instead, he attacked the Persian center, where Darius was, and relied on cavalry to protect his flanks.
This was a typical calculated gamble on Alexander's part. He was gambling that if he broke the Persian center, the rest would dissolve, and he was calculating that his soldiers were superior enough to deliver the blow.
He was right, of course. Once again Alexander led the charge on Darius himself and again Darius panicked and ran away, and once again the rest of the Persian army evaporated. And, once again, Darius escaped, despite a furious pursuit by Alexander that lasted three days.
Occupation of Persia
Alexander now entered the Persian Empire. Babylon welcomed him as liberator. The sacred Pharsi city of Susa resisted and fell to a siege. Alexander ordered the city burned. He went on to occupy Persis, the capitol city and at last sat on the Persian throne of Darius.
Alexander now ruled the largest empire the Western world had ever seen, but he could not rest secure, for Darius was still a threat. As long as Darius remained alive, Alexander would not be able to claim his titles.
After arranging affairs in Persia, Alexander set off in pursuit. Darius fled, keeping a few steps ahead of the Greeks. He entered Bactria and sent word ahead to its king, asking for his aid.
The Bactrian king assessed the odds and made his decision. A few days later, Alexander found Darius dead by the roadside (330).
