“My name is Legion: for we are many” (St. Mark v. 9). A
proverbial expression somewhat similar to hydraheaded. Thus, speaking
of the houseless poor we should say, “Their name is Legion;” so also we
should say of the diseases arising from want of cleanliness, the evils
of ignorance, and so on.
The Thundering Legion.
The Roman legion that discomfited the Marcomanni in 179 is so
called, because (as the legend informs us) a thunderstorm was sent in
answer to the prayers of certain Christians; this storm relieved the
thirst of the legion. In like manner a hail-storm was sent to the aid
of Joshua, at the time when he commanded the sun to stay its course,
and assisted the Israelites to their victory. (Dion Cassius, lxxi. 8.) (See Joshua x. 10-12.)
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894