Each book was special and took a long time to make. Sometimes a monk worked for a year or more on one book. Usually they were stories from the Bible, so the monks wanted them to be very beautiful. They decorated the letters and the borders of their books. Today these one-of-a-kind books are called "illuminated manuscripts."
This is a page from The Book of Kells. It was made by Irish monks about 1200 years ago. Some of the letters are made with real gold. Do you see how the border turns into an animal? What kind of animal do you think it is? Look at the letter "T" at the top of the page. What do you notice about it?