Where did they keep the mules in garrison?

[D B Campbell]

Surely an army in garrison has need of only a moderate number of mules, compared to on the march when the regiment was fully mobilised.

Hence my reason for pointing out:

Many legions would've had absolutely no use for mules, in any case.

... that suggestion is most improbable. Of course, on occasion there might be a shortage of mules, but it would be fairly safe to say that mules were present in all Roman Armies, and that their total absence would be an extreme rarity, if it ever occurred.

But this idea was abruptly shot down as "most improbable". :|