Voltaire's views about Islam were generally negative, and he found its holy book, the Quran, to be ignorant of the laws of physics. In a 1740 letter to Frederick II of Prussia, Voltaire ascribes to Muhammad a brutality that "is assuredly nothing any man can excuse" and suggests that his following stemmed from superstition; Voltaire continued, "But that a camel-merchant should stir up insurrection in his village; that in league with some miserable followers he persuades them that he talks with the angel Gabriel; that he boasts of having been carried to heaven, where he received in part this unintelligible book, each page of which makes common sense shudder; that, to pay homage to this book, he delivers his country to iron and flame; that he cuts the throats of fathers and kidnaps daughters; that he gives to the defeated the choice of his religion or death: this is assuredly nothing any man can excuse, at least if he was not born a Turk, or if superstition has not extinguished all natural light in him."