After this he says that Alexander led on his army in an extended line, being then at a distance of about forty stades from the enemy.
It is difficult to conceive anything more absurd than this. Where, especially in <a class="linkToPlace" target="_blank" href="/place?placename=Cilicia&groupId=467&placeId=350">Cilicia</a>, could one find an extent of ground where a phalanx with its long spears could advance for forty stades in a line twenty stades long?
The obstacles indeed to such a formation and such a movement are so many that it would be difficult to enumerate them all, a single one mentioned by Callisthenes himself being sufficient to convince us of its impossibility.
For he tells us that the torrents descending the mountains have formed so many clefts in the plain that most of the Persians in their flight perished in such fissures.
But, it may be said, Alexander wished to be prepared for the appearance of the enemy.
And what can be less prepared than a phalanx advancing in line but broken and disunited? How much easier indeed it would have been to develop from proper marching-order into order of battle than to straighten out and prepare for action on thickly wooded and fissured ground a broken line with numerous gaps in it
It would, therefore, have been considerably better to form a proper double or quadruple phalanx, for which it was not impossible to find marching room and which it would have been quite easy to get into order of battle expeditiously enough, as he was enabled through his scouts to receive in good time warning of the approach of the enemy.
But, other things apart, Alexander did not even, according to Callisthenes, send his cavalry on in front when advancing in line over flat ground, but apparently placed them alongside the infantry.
Walbank Commentary