The first books then were formed of sheets of paper or parchment, laboriously printed from xylographic blocks, that is to say wooden blocks on which a _tailleur d'images_ had left in relief the designs and the letters of the text. He had thus to trace his characters in reverse, so that they could be reproduced as written; he had to avoid faults, because a phrase once done, well or ill, lasted. It was doubtless this difficulty of correction that gave the idea of movable types. If the cutter seriously erred, it was necessary to cancel altogether the faulty block. This at least explains the legend of Laurent Coster, of Haarlem, who, according to Hadrian Junius, his compatriot, discovered by accident the secret of separate types while playing with his children. And if the legend of which we speak contains the least truth, it must be found in the sense above indicated, that is in the correction of faults, rather than in the innocent game of a merchant of Haarlem. However, we shall have occasion to return to the subject of these remarks. It should be well established that engraving in relief on wood alone gave the idea of making xylographic blocks and of composing books. Movable type, the capital point of printing, the pivot of the art of the Book, developed itself little by little, according to needs, when there was occasion to correct an erroneous inscription; but, in any case, its origin is unknown. Doubtless to vary the text, means were found to replace entire phrases by other phrases, preserving the original figures; and thus the light dawned upon these craftsmen, occupied in the manufacture and sale of their books.