Which battle in 331 BCE ended Achaemenid Persian rule after Alexander defeated Darius III?

The Battle of Gaugamela in 331 BCE ended Achaemenid Persian rule after Alexander the Great defeated Darius III.

The battle took place near Arbela in northern Mesopotamia, in territory corresponding to modern Iraq. Darius selected relatively open ground to make better use of cavalry and scythed chariots, while Alexander organized a smaller but highly trained Macedonian force.

Alexander’s breakthrough toward Darius caused the Persian king to flee, and the defeat destroyed the empire’s ability to coordinate resistance. Darius was later killed by one of his own nobles, Bessus. Alexander then occupied major Persian centers, including Babylon, Susa, and Persepolis. Gaugamela is therefore often treated as the decisive military collapse of the Achaemenid Empire.