Where did they keep the mules in garrison?

[Carvettia]

Can't tell you how many mules or other equids were typical per fort, but there's a paper called "Where did they keep the horses" based on the archaeo at Wallsend (Segedunum). Hodgson, N. & B. Griffiths 1999 ‘Wallsend: Where did they keep the Horses in Roman Forts?’ Current Archaeology 164: 234-289

I incorporated some of this into a web page of my own ( http://www.fellpony.f9.co.uk/fells/rom_dark/cavalry.htm )

Stabling was re-excavated by Tyne and Wear Museum staff in 1999-2000 at South Shields (Arbeia) and in 1998 at Wallsend (Segedunum; see artist's impression >>). The centralised, oblong drainage pits found there suggest that the stables were intended to house male horses rather than female. The roughly square outline of ~10 x 12 Roman feet (3.6 metres) which was allowed for three troopers, gave each horse (pony) a stall space 4 feet wide by 10 feet long. The nine stables in each barrack block would house 27 horses of a 30-strong "turma", with 3 officers (principales) and their horses accommodated at the end of the range in a slightly larger space. Horses may have been tied up outside the stables on a regular basis as there is further drainage provision outside each building. Hodgson cites Sommer (1999a) who points out that cavalry mounts would have had daily work and exercise outside; this apparently small space may have been perfectly adequate because the horses were kept in readiness for instant action and might spend long stretches of the day working hard. In addition the stables would rarely be full since the troops would be out working. The horsemen evidently lived in the same barrack, backing onto the stalls at ground level, while their servants (calones) lived above in attics. These must have been unenviable places to live - full of smoke from the calvalrymen's fires and of the smell of ammonia from the horses below!