You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
alternatehistory.com
Darius III sees the initial attack as a feint that it is and slams into Alexander's main attack with the Greek Mercenaries and kill Alexander.
The battle then becomes an utter disaster and route for the Macedonians as the Persians have already captured their supplies and cut off their escape route. So they either surrender or die.