Battle of Gaugamela

On October 1, 331 BC, Alexander the Great defeated Darius III of Persia in the Battle of Gaugamela. An excerpt from the article:

"Battle of Gaugamel

The Battle of Gaugamela (1st October 331 BCE, also known as the Battle of Arbela) was the final meeting between Alexander the Great of Macedon and King Darius III of Persia. After this victory, Alexander was, without question, the King of all Asia. Gaugamela (means "The Camel's House") was a village on the banks of the river Bumodus. The site of the battle is thought to be Tel Gomel (Hebrew - "Camels Mount") in northern Iraq.

Alexander's Campaign
Following the assassination of Phillip II, his father, in 336 BCE, Alexander and his army left their home of Macedonia for the last time and set out on a goal of conquering all of Persia. After crossing the Hellespont, Alexander traveled northward where he met and defeated the Persians under the leadership of the Greek mercenary Memnon at the Battle of River Granicus. As in future meetings with Alexander, Darius and his generals continually underestimated the abilities of the young Alexander. He was considered by many, even those in Greece, to be nothing more than an upstart.

Darius offered Alexander half of his kingdom; however, Alexander rejected the offer by simply saying there could never be two suns.
From the River Granicus Alexander moved southward along the coast of Asia Minor to Halicarnassus where he defeated Memnon for the second time. Finally, after waiting for over a year, Alexander and his forces met Darius at Issus in November of 333 BCE where, again, the Persians suffered defeat. Even more embarrassing for Darius was that Alexander captured his family - his mother, wife, and daughters. Wishing to avoid further conflict (and hoping to regain his family), Darius offered Alexander half of his kingdom and even his daughter's hand in marriage; however, Alexander rejected the offer by simply saying there could never be two suns - it would upset the world order. Alexander also challenged the Persian king to face him again in battle.