Voltaire and the Marquise also studied history, particularly the great contributors to civilization. Voltaire's second essay in English had been "Essay upon the Civil Wars in France". It was followed by "La Henriade", an epic poem on the French King Henri IV, glorifying his attempt to end the Catholic-Protestant massacres with the Edict of Nantes, which established religious toleration. There followed a historical novel on King Charles XII of Sweden. These, along with his "Letters on the English", mark the beginning of Voltaire's open criticism of intolerance and established religions. Voltaire and the Marquise also explored philosophy, particularly metaphysical questions concerning the existence of God and the soul. Voltaire and the Marquise analyzed the Bible and concluded that much of its content was dubious. Voltaire's critical views on religion led to his belief in separation of church and state and religious freedom, ideas that he had formed after his stay in England.