The cavalry was the only arm in which the Persians were not greatly at a disadvantage; and cavalry alone cannot gain, or even save a battle.
When Darius put himself into a position where he lost all the advantages derivable from superiority of numbers, he made his own defeat and his adversary's triumph certain.
It remained, therefore, before the Empire could be considered as entirely lost, that this error should be corrected, this false step retrieved.

All hope for Persia was not gone, so long as her full force had not been met and defeated in a fair and open field.

When Darius fled from Issus, it was not simply to preserve for a few months longer his own wretched life; it was to make an effort to redeem the past--to give his country that last chance of maintaining her independence which she had a right to claim at his hands--to try what the award of battle would be under the circumstances which he had fair grounds for regarding as the most favorable possible to his own side and the most disadvantageous to his adversary.

Before the heart of the Empire could be reached from the West, the wide Mesopotamian plain had to be traversed--there, in those vast flats, across which the enemy must come, a position might be chosen where there would be room for the largest numbers that even his enormous Empire could furnish--where cavalry and even chariots would be everywhere free to act--where consequently he might engage the puny force of his antagonist to the greatest advantage, outflank it, envelop it, and perhaps destroy it.

Darius would have been inexcusable had he given up the contest without trying this last chance--the chance of a battle in the open field with the full collected force of Persia.
His adversary gave him ample time to prepare for this final struggle.
The battle of Issus was fought in November, B.C.333.