This is a special book from the early Middle Ages (France, 9th century). Not only does it contain a high volume of very attractive images, but these images are also not what you would expect: they are drawn, as it were, with words. They illustrate Cicero’s Aratea, a work of astronomy. Each animal represents a constellation and the written words in them are taken from an explanatory text by Hyginus (his Astronomica). His words are crucial for these images because the drawings would not exist without them. It is not often in medieval books that image and text have such a symbiotic relationship, each depending on the other for its very existence.Image and text from Erik Kwakkel's excellent blog. At the link you will find five additional images of similarly-illustrated animals, and links to the digitized primary source and related materials.
Reposted from 2013 to note that the Public Domain Review has posted a gallery of sixteen of these "calligrams."