From single prints, with letter-press inscriptions, the next stage, that of a series of prints accompanied by letter-press, was obvious.  Such are our first recognized block-books, among which are the Apocalypse, and the Biblia Pauperum (or Poor Man’s Bible), supposed to have been printed at Haarlem by Laurence Koster, between 1420 and 1430; I say supposed, because we have no positive evidence either of the person, place, or date; and Erasmus, who was born at Rotterdam in 1467, and always ready to advance the honor of his country, is silent on the subject.  We rely chiefly upon the testimony of Ulric Zell, an eminent printer of Cologne, who is quoted in the Cologne Chronicle of 1499, and Hadrian Junius, a Dutch historian of repute, who wrote in the next century.  Both agree in ascribing the invention of book-printing from wooden blocks, as well as the first germ of movable wood and metallic type printing, to Haarlem; and Junius adds the name of Laurence Koster.  His surname of Koster is derived from his office, which was that of custodian, sexton, or warden of the Cathedral Church of Haarlem.  The story told of the accident by which the discovery was made is as follows: 

Koster, as he was one day walking in a wood adjoining the city, about the year 1420, cut some letters on the bark of a beech tree, from which he took impressions on paper for the amusement of his brother-in-law’s children.  The idea then struck him of enlarging their application; and, being a man of an ingenious turn, he invented a thicker and more tenacious ink than was in common use, which blotted, and began to print figures from wooden tablets or blocks, to which he added several lines of letters, first solid, and then separate or movable.  These wooden types are said to have been fastened together with string.

One thing seems pretty clear, which is, that, whether or not Koster was the printer, the first block-books were produced somewhere in Holland, as several are in Dutch, a language seldom, if ever, printed out of its own country.  They were generally printed in light-brown ink, like a sepia drawing, which, I think, was adopted with a view to their being colored—­a condition in which we find the greater part of them.  When these prints were colored they presented very much the appearance of the Low Country stained-glass windows.

Block-books continued to be printed and reprinted, first in Holland and afterward in Germany, with considerable activity, for twenty or thirty years, during which period we had several editions of the Biblia Pauperum, the Ars Moriendi (or Art of Dying), the Speculum Humanae Salvationis, and many others, chiefly devoted to the promulgation of scripture history.  The earliest ones are printed, or rather transferred by friction—­and therefore on one side only of the paper—­entirely from solid blocks; later on, some portions were printed with movable types of wood; and at last the letter-press was entirely of movable metal types.  Junius says that Koster by degrees exchanged his wooden types for leaden ones, and these for pewter; and I will add that it is not unlikely they may have been cast in lead or pewter plates from the wooden blocks, as metal-casting was well understood at the time.