Where did they keep the mules in garrison?

[Paralus]

Question, is there any consensus about how many animals single legion had?

People are free to speculate, of course. But in truth, we have absolutely no idea how many mules a single legion might have. And many legions would've had absolutely no use for mules, in any case. Even taking a hypothetical "legion at war", Jonathan Roth believes that each tent-party required two mules, while others imagine that they had only one mule -- there's a doubling of the figures, right there!

John F. Shean ( Hannibal's Mules: The Logistical Limitations of Hannibal's Army and the Battle of Cannae, 216 B.C.) whilst not discussing a legion at war, presents some interesting figures for Hanibal’s army of invasion. These are based on Engel’s work in Alexander the Great and the Logistics of the Macedonian Army. Although published in 1978 it is, as far as I’m aware, still the fundamental work on ancient logistics and what applied to Alexander’s army likely also applied to Hannibal’s.

Shean assumes no wagons – the sources not mentioning same and the Alps crossing almost certainly precluding same – and so the supply train was carted by mule. This being the case he calculates that the army of invasion (90,000 infantry; 12,000 horse Pol 3.35.1-2) will have needed mules in the order of (day’s provisioning / mules): one day - 2,922; one week - 29,895; ten days - 55,520. He gives figures for the other stages of the invasion and, lastly, for the immediate post-Cannae army (34,500 infantry; 9,800 horse Pol.3.114.5; 117.6): one day - 1,509; one week - 15,443; ten days - 28,680.

Dry as oxen fodder, I know. More interesting is the well reasoned – and source-based – argument for Hannibal’s “failure” to move on and take Rome after either Trasimene or Cannae. Dead simple:

Generations of writers and historians have either ignored or missed much of the ancient literary evidence concerning Hannibal's supply problems. Despite all the speculation on grand strategy, personality defects or siege equipment, Hannibal's failure to move on Rome stemmed from the least glamorous and most mundane reason of all: no food

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As Shean notes, Hannibal’s army spent much time in Italy “living hand to mouth”.