legion (and legions of followers)

Drawn into English from Old French in the 13 Century legere (to choose), from the Latin legio, history and longevity are inherent in this noun.

Initially, it referred to a specific Roman military unit of infantry supported with cavalry which ranged from 3 to 6 thousand men.

It expanded its meaning to apply to any large military force e.g the French Foreign Legion.

Then it shifted into being an association of ex-servicemen eg the British Legion.

Currently, but not exclusively it refers to a large mass, usually of people as in ‘a legion of followers’. 

Increasingly, I see it applied to other ‘masses’ or ‘groups’ especially as an exaggeration in humorous contexts; for instance, ‘a legion of horseflies at the Melbourne Cup’.