In Europe, wood block printing was being practiced by the 14th century at the latest. It has been said, however, that the wood block print known as the oldest is the "Virgin and Child with Four Saints" that was printed in 1418. Since many woodprints printed around the same era, including the one mentioned above, were religious paintings designed for the common people, and only a small number of them are still in existence, the details of their printers and other related matters are not known. From these woodprints emerged printed broadsides that contained not only pictures but also text, and eventually, people started to bind several broadsides together to make a booklet. These booklets are called "block books" or "xylographs," which are distinguished from incunabula. The block books that were most frequently printed include Biblia pauperum, Speculum humanae salvationis, Apocalypse and Ars moriendi, which were also printed as incunabula. Block books were not necessarily old, and many of them were printed during the period 1465-1475. One of the distinctive features of block books is that only one side of the paper was printed, but in some cases, the blank backs were pasted together to make a book without blank pages.