The Macedonians (who were grossly outnumbered) wanted to attack the Persians at night, but Alexander would not take advantage of Darius' vulnerability. Believing he would ultimately defeat the Persian ruler, Philip's son wanted to face his enemy on the battlefield in the light of day. Only then, he reasoned, after a fairly fought fight, would Darius cease to wage war against the Macedonians.
The exact location of the Gaugamela battle is not clear. Many scholars think it was at Tel Gomel which is east of modern Mosul. Historical descriptions paint the scene as just east of the Tigris River. The fighting took place in October, 331 B.C.
Darius wanted to fight on a flat plain which would benefit his numerically superior and specially recruited cavalry forces. He also used scythed chariots and, before the battle, ordered bushes and vegetation removed from the battlefield to maximize the chariots' effectiveness.
Before the Battle of Gaugamela, Macedonians had never seen elephants. Darius used about fifteen of them - some scholars think the number was as high as fifty - supported by Indian chariots. Alexander, meanwhile, personally commanded the Macedonian right flank.
Alexander's men slaughtered the Persians, but once again Darius escaped - this time due, in large part, to strategic mistakes by Parmenion, Alexander's general. The former Persian emperor fled to Arbela (modern-day Arbil). (Note, however, the contemporary story of the battle, written on a cuneiform tablet, which states that Darius' troops deserted him. See, especially, note 8.)
A Macedonian had thus supplanted the Persian Emperor as a ruler in Asia. Alexander was crowned in a lavish ceremony in Arbela. Darius, still on the run, was gone from the city by the time the Macedonians arrived. Alexander sent letters to all Greek cities in Asia Minor, advising them that he had banished tyranny from the land.
The rich cities of Babylon and Susa were the next Persian towns to fall. When he reached Persepolis, capital of the Persian Empire, Alexander allowed his army to rest. Four months later, before they left Persepolis, the Macedonians burned the royal palace.
Alexander, it is said, came to regret the massive damage he ordered to Persepolis and other places in the Persian Empire. Scholars speculate that, had he lived a longer life, perhaps he would have ordered repairs.
In 330, trouble developed in Alexander's inner circle. Allegations of a plot to kill him were brought against some of his officers, including Philotas, a lifelong friend. He was shortly executed.
Months later, after a night of heavy drinking, Alexander's close friend Cleitus, son of Parmenion, hurtled insults against him. Annoyed, Alexander ran his spear through Cleitus. When he realized he'd killed his close Companion, Alexander was so upset he nearly committed suicide.
Following the rest at Persepolis, Alexander continued to pursue Darius. When he finally caught up with him, Darius was already dead. His own men had killed him in his coach.
Alexander rewarded the assassin's treachery with execution but gave Darius a royal funeral. Even so, Alexander - seen through Persian eyes - was never that "great."
Although Alexander and his men were winning victory after victory in Persia, there were major differences between Greek and Persian culture. Trying to reconcile some of those disparities, Alexander married Roxane, a Persian woman from Bactria (today's northern Afghanistan). He encouraged his men to likewise marry Persian women.
Some of Alexander's troops thought their leader had gone too far when he began to wear Persian instead of Macedonian clothing. The sheer force of his magnetic personality, however, convinced them to stick with their general.
He would next lead them to battle in India, the land of elephants.