_Frederick II._ is called the Royal Free-thinker; and yet the general introduction of the book censure into Prussia occurred precisely during his reign. The first general censure edict was issued in 1749 and remained in force till the death of the king. All books, even those printed in foreign tongues, were subject to the censure. Even all episcopal and Papal proclamations were subjected to the royal censure. That the leaders in the Reformation and their successors were not prevented by their avowal of the principle of free research from exercising rigorous, often tyrannical, censure, not only against the Catholics but also against their fellow reformers, is well known. _M. Lehmann_ writes in the Preuss. Jahrb. 1902: “It claims to be infallible, this Papal Church, it wants to be to the faithful everything, in science and even in nationality. It offends every nation. The Index in the shape given it in 1900 by the present Pope proscribes the ‘Oeuvres du Philosophe de Sanssouci,’ _Kant’s_ ‘Critique of Pure Reason,’ _Ranke’s_ ‘History of the Popes,’ the greatest German king, the greatest German philosopher, and the greatest German historian” (1902, no. 8). As to _Frederick II._, his own works appeared only after his death in 1788, and even then only in part; later on there were other editions. None of these is put on the Index. On this list we find since 1760 the “Oeuvres du Philosophe de Sanssouci.” Under this title appeared at first three volumes, in but a few copies, intended for the most intimate friends of the king. The first volume he soon withdrew and had it burned of his own accord; it contained the “Palladion” an imitation of Voltaire’s “Pucelle,” a salacious work throughout. In 1762 a new edition was issued. It also contains a philosophical treatise denying the immortality of the soul; this treatise was also published separately and specially prohibited in 1767. A third work put on the Index is a spurious attack on the Popes published by order of King _Frederick II._, with a preface by him. Its author is said to have been the French abbé _Jean Martin De Prades_, reader to the king. These are the indicted works of _Frederick II._, all written in French and in substance French Voltairianism. Thus came the greatest German king on the Index! _Ranke’s_ “Roemische Paepste” is on the Index, because the book belittles the constitutions and doctrines of the Catholic Church: not because of the true things the author says about Popes. _Von Pastor’s_ “History of the Popes” is not on the Index, notwithstanding the bitter truths he writes about Popes _Alexander VI._ and _Leo X._