According to Wikipedia the site is not precisely known but this is best estimate.
The Battle of Gaugamela (pron.: /ˌɡɔːɡəˈmiːlə/; Greek: Γαυγάμηλα) took place in 331 BC between Alexander the Great and Darius III of Persia. The battle, which is also called the Battle of Arbela, resulted in a decisive victory for the Macedonians and led to the fall of the Persian Empire.