This past February, librarians at the Russian State Polytechnical Museum Library in Moscow were preparing their collection for relocation to a temporary depository when they made a surprising discovery. Behind one of the emptied stacks a librarian noticed a plywood wall that sounded hollow when knocked upon. The cover was moved aside and revealed a number of books. As librarians dug deeper and removed the entire wall, they uncovered a 6.5 foot long hiding place that housed 30,000 books printed before the Russian Revolution in 1917. The books were almost exclusively in foreign languages. Svetlana Kukhtevich, deputy director of the Polytechnic Library, explained that "scientists and generally educated people of the 19th century spoke several languages and there was no need to publish books in Russian." The majority of the books were printed in the late 19th and early 20th century, but the oldest book in the collection, "Description of Picteresque Areas Occupied by Germany", was published in 1706. (Don't you love the titles of 18th century books?!) The state fund was responsible for all book collections nationalized during and following the revolution, and most of the hidden books were transferred to the Polytechnical Library from the fund. A number of volumes still contained bookplates, which indicate the original owners. The best part is that librarians later discovered another hollow sounding plywood wall within the archives that revealed two additional niches stuffed with 19th century periodicals on the history of science and technology, art, and architecture. Museum librarians are puzzled as to why the books would have been hidden. "We had an idea that there was a cache with books somewhere in the library but we didn’t know exactly where," Kukhtevich said. "The previous director worked here for 30 years and never found anything."