As the investiture controversy rages on, Pope Gregory VII and King Henry IV face off, forcing one to yield to the other. While the eastern empire is being overrun by Seljuk Turks, Gregory’s successor, Urban II, assumes the papal throne and, preaching at the Council of Clermont, initiates the First Crusade, which draws 60,000—peasants and nobles alike—to the cause of vanquishing the Arab and Turkish infidels.