Between 1596 and 1647, art dealer and diplomat Philipp Hainhofer traveled around Europe collecting signatures in the “Große Stammbuch,” or “Album Amicorum.” Similar to an autograph book, Hainhofer’s register includes the marks of Cosimo II de Medici, Holy Roman Emperor Rudolf II, and Christian IV of Denmark and Norway, to name a few. On August 25 the Herzog August Bibliothek purchased the book—which was thought to be lost until it emerged in a London auction in 1931—for about $3.1 million.