Horses @ the Morranon

[Essex]

If you think it's a mistake for not showing the horses 'departing' then Tolkien makes the same 'mistake'.

From The Black Gate Opens after Sauron springs his trap:

The Captains mounted again and rode back............... (next paragraph we then hear of Aragorn next...)Little time was left to Aragorn for the ordering of his battle. Upon the one hill he stood with Gandalf, and there fair and desperate was raised the banner of the Tree and Stars

We never hear mention of the Horses again, or any men mounted on them.

You can't show EVERYTHING. You know, maybe even one of the men of the West had to go to the toilet before the battle started, but thank the Stars we didn't see that!