It's six books in one!

Medieval bookbinders may have been the precursors of eReaders when they developed the dos-à-dos (or "back-to-back") book with two or more separate texts and multi-hinged covers. One example is the beautiful devotional dos-à-dos book owned by the National Library of Sweden which includes six works. (photos)

The Swedish example was printed in Germany in the 16th century and includes Martin Luther's Der kleine Catechismus and other religious texts.