Ironsides

Webster's Dictionary

(n. /) A cuirassier or cuirassiers; also, hardy veteran soldiers; - applied specifically to Cromwell's cavalry.

The Nuttall Encyclopedia

Cromwell's troopers, a thousand strong, and raised by him in the Eastern counties of England, so called at first from the invincibility displayed by them at Marston Moor; were selected by Cromwell "as men," he says, "that had the fear of God before them, and made conscience of what they did.... They were never beaten," he adds, "and wherever they were engaged against the enemy, they beat continually."