The National Library of Brazil holds the largest collection of books in South America. Although there are many intriguing volumes on its shelves, I found the library most notable not for any particular book but for the way it sorts its books. The great algorithm? The books are sorted by size, placed wherever they’ll fit.

This seemingly arbitrary sorting algorithm, which sorts neither alphabetically by author nor title, had an unexpected advantage: when the government tried to censor books before the digital age, librarians had only to hide the cards that contained the books’ locations and the books to be censored became unfindable by those wishing to destroy them.