William Cavandish, Duke of Newcastle, was an English nobleman, playwright, poet and patron of the arts. An ally of Charles I, he fled England after the King was executed, and was exiled to Belgium where he established an influential stable and wrote A General System of Horsemanship.

REF: The Classical Tradition – Out of the Dark Ages – Riding as Art – The Masters of High School by Chris Hector

Shoulder In – Its invention and its purpose by H. L. M van Schaik