Where did they keep the mules in garrison?

[Gaius Julius Caesar]

Apparently it has been used to identify the location where horses were kept, i.e. in the same building as the cavelrymen.

Of course, that's in a permanent fort site, Byron. You'll find details in my Roman Auxiliary Forts book (but not in the very out-of-date fort books by Roger Wilson and Anne Johnston, that were advertised on another thread).
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That would be where I read it, thanks for the jog...