 Darius did attempt to restore his once great army after his defeat at the hands of Alexander, but he failed to raise a force comparable to that which had fought at Gaugamela, partly because the defeat had undermined his authority, and also because Alexander's liberal policy, for instance in Babylonia and in Persis, offered an acceptable alternative to Persian policies.When at Ecbatana, Darius learned of Alexander's approaching army, he decided to retreat to Bactria where he could better use his cavalry and mercenary forces on the more even ground of the plains of Asia.He led his army through the Caspian Gates, the main road through the mountains that would work to slow a following army.