Mesmerizing Miniatures via Atlas Obscura.
In 1896, the Salmin Brothers, a Padua-based publishing company, produced Galileo a Madama Cristina de Lorena (Galileo’s Letter to Christina). It had an embossed cover and slipcase, but it had another, exceptional feature: It was sized at just 0.7 by 0.4 inches. Within, the text is printed in “fly’s eye type,” which is so small that when the Salmin Brothers first used it, for Dante’s Divine Comedy, it reportedly damaged the eyesight of the typesetter. This time, it was used in a title about one-third the size of the previous example—the smallest book ever printed with hand-set, movable type.
Source: Adafruit – Art