E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
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. 1012.)