"Illuminated." It means lit up, flooded with light. So what's an illuminated manuscript, other than one sitting on your desk with a bright desk lamp?
Actually it means something somewhat different. A medieval illuminated manuscript is one with drawings and paintings in it. Because, you remember, the printing press was only invented at the end of the Middle Ages, medieval books were all unique productions. They were copied by hand, mostly on parchment before the fourteenth century, and they were special and valuable. Drawings and other images made them even more special.
For something like a Bible, it was considered appropriate to be especially prolific with images. One of the most common forms of illumination was to make the initial letter of a section into a little picture. This is a capital D (for Deus, God) from a ninth-century book of Psalms, done at the monastery of Corbie (eastern France).
Full page illustrations were also found, though less commonly. Sometimes (like here) they would be in a few subdued colors, but other times they would be done in vivid colors. Usually the copying of the text and the drawing of the illuminations would be done separately, by different people. There are plenty of medieval manuscripts where the person who was supposed to be drawing the fancy initials started but then never got back to the project, because there are big blanks where an illuminated initial is supposed to be.
Those doing the illuminations seem sometimes to have gotten bored with their careful, devout images and started drawing little scenes in the margins, demons, cats, people with faces in unusual parts of their anatomy, horses, or whatever took their fancy. Usually these do not show up in Bibles, but they were common in illuminated books of history and the like.
When the Middle Ages became popular and romantic in the nineteenth century, wealthy people started collecting illuminated initials. They would even have scrapbooks, where they would carefully cut an especially nice initial out of a medieval manuscript and paste it into their scrapbook, then toss the now-mutilated piece of parchment. This makes medievalists' stomachs hurt just to think about it.
© C. Dale Brittain 2023
For more on medieval manuscripts and other aspects of medieval history, see my ebook Positively Medieval, available on Amazon and other ebook platforms. Also available in paperback.