At a comparatively early period, probably as early as the first part of the 12th century, there came a call for the dissemination of knowledge in somewhat rudimentary form among the common people. At an earlier period still this desire had expressed itself in the elaborate sculpture and stained glass with which the churches were decorated. The church itself was the poor man's Bible and his library the lives of saints and martyrs. The story was told to him by the priest. It was visualized by the artist. Conventional types or attributes of biblical and other personages were adopted so that the peasant or the artisan could recognize anywhere the figure of Christ, of one of the evangelists, of Moses, or of the patron saint of his church or city. The clergy and the lettered classes had long been accustomed to the pictures which not only decorated but interpreted the pages of their books. It was only natural that there should be a desire to have at least these pictures in the hands of the people so as to reinforce in the home the teachings of the church. The multiplication of these pictures, so costly and so tedious in their production, was clearly out of the question, but why not make a stamp big enough to carry a picture of a saint or a simple biblical scene, make an impression from it on vellum and so produce a rude but cheap picture which could be multiplied indefinitely and sold at a low rate? No one knows who invented this idea or who first practised making these picture sheets. We know, however, that such sheets were printed as early as the 12th century. Originally printed upon cloth or vellum, by the middle of the 14th century they came to be printed on paper, and by the early part of the 15th they had become very common. Circulated at first only in single leaves, at a later period the leaves were folded and combined into quires as in other books and we have the fully developed block book as it is called, each leaf being printed from a single plate.