The fall of the Achaemenid Empire was driven by internal instability, civil war, and the loss of its administrative cohesion after the looting of Persepolis.

“The gold looted from the treasuries of Pipilis supposedly weighed 120,000 talents or nearly 4,000 tons. The Macedonians needed thousands of camels to carry it away. This gold had been the treasury of the empire that kept its welloiled machine running. And in looting it, Alexander had ripped the hear”