ABSTRACT
The uneven distribution of cavalry, both alae and cohortes equitatae, along the European frontiers of the Roman Empire in the second century, is examined and compared with that of the Late Empire. Although partly a matter of suitability of terrain, other factors operated in the earlier period. Cavalry was sited to control routes and lines of advance, as well as important trade routes and potential threats. In some cases alae were sited near legionary bases, thus creating a formidable mixture of heavy infantry and cavalry forces both for offensive and defensive action. In the fourth century the pattern reflects the changed character of the perceived threat. There was a considerable increase in the number of cavalry units on the Middle Danube and they were more evenly spread. In Britain infantry predominated along Hadrian's Wall, suggesting that here the nature of the external danger was different. More research is needed.
