In Europe, as in China, the first printing was done by means of a block, that is, a slab of wood on which the design was carved in relief, and from which, when inked, an impression could be transferred to paper or other material. This process is known as block-printing, and in Europe was principally used for the production of illustrations, the text, which came to be added later, being accessory and subordinate to the picture. The first European block-prints are pictures of saints, roughly printed on a leaf of paper and usually rudely coloured. Heinecken, whose _Idée general d'une Collection complette d'Estampes_ (1771) is still a standard work, is of opinion that pictures of this class were first executed by the old makers of playing-cards, and that the playing-cards themselves were printed from wood and not drawn separately by hand. In this case the cards should rank as the earliest examples of block-printing, or wood-engraving. Heinecken has not been alone in entertaining this opinion, but, on the other hand, there are some who consider that the portraits represent the first woodcuts, and that the early playing-cards were drawn and painted by hand. The single-leaf portraits of saints were produced chiefly, or perhaps solely, in Germany, and examples are now rare. It is curious that most of those which have survived to the present day have been found in German religious houses, pasted inside the covers of old books, and thus shielded from the destruction to which their fragile nature rendered them liable. One specimen, which has the reputation of being the earliest extant with which a date can be connected, is the well-known St Christopher, which represents the saint carrying the child Christ over a stream, after an old legend. This specimen bears the date 1423, and was discovered pasted in the cover of a mediæval manuscript in the monastery at Buxheim, in Swabia, and is now in the John Rylands Library at Manchester. The date, however, may be only that of the engraving of the block, and not the year of printing. A theory was put forward by Mr H. F. Holt, at the meeting of the British Archaeological Association in 1868, that this St Christopher, so far from being the earliest known specimen of printing of any sort, belonged to a period subsequent to the invention of typography, and that the date 1423 refers only to the jubilee year of the saint, and not to the execution of the print. He also held that the block-books, to which we refer below, were not the predecessors of type-printed books, as they are usually considered to be, but merely cheap substitutes for the costly works of the early printers. But these theories, though not disproved, do not receive the support of bibliographers in general.