Explanation: The Romans in the Late Empire often seemed to have trouble mustering the forces to combat barbarian incursions, but curiously always seemed ready to rumble for the Imperial title...
Limitanei were border patrol troops instituted late in the Empire, after the decline of the Roman Legions, The Roman Legions were professional and served limited terms. Limitanei, on the other hand, were often poorly trained and equipped (and poorly compensated), conscripted for life. For obvious reasons, this was not a popular job, so a large number of prospective recruits would cut off one of their thumbs to make themselves unsuitable for conscription - something which would become so widespread that the death penalty was imposed for doing so intentionally.
'Scout equites' are a unit from the game Total War: Atilla, and while they are only of marginal historicity (ie only insofar as Roman units included scouts who were mounted), they're part of every garrison, and the only troop worth a good goddamn when the barbarians come knocking, lmao.