In the heart of the Middle Ages, just when they were working up to their most splendid phase, the great thirteenth century, there arose — and was for the moment completely defeated — a singular and powerful attack upon the Catholic Church and all the culture for which it stood. This was an attack, not only on the religion that made our civilization, but on that civilization, itself; and its general name in history is "The Albigensian Heresy." In the case of this great struggle we must proceed as in the case of all our other examples by first examining...