The Book of Kells
Folio 29r, part of the introduction to the Gospel of Matthew
Late 8th to early 9th century.

The Book of Kells (which is named after the Southern Irish monastery which owned it) is a truly amazing piece of art and craftsmanship. It is an extraordinarily detailed illuminated manuscript containing the gospels of Matthew, Mark, Luke and John (although sections of John are missing), as well as images of the evangelists, depictions of the Virgin Mary and Christ, and canon tables, all elaborately and intricately decorated. The lavish ornamentation found in the Book of Kells is far greater than any other surviving Irish-English Gospel Books.
The book would have been used much more for sacramental purposes rather than educational. There are numerous uncorrected mistakes in the text (the artists often had to write from memory due to the scarcity of bibles), and practical matters such as headings on canon tables were often abandoned if they didn’t sit favorably with the aesthetic intentions of the artists. These intentions were to create an astoundingly intricate collection of religious decoration. Some sections of the manuscript are so detailed they can only truly be appreciated with a magnifying glass. In one square inch of manuscript it is possible to count 158 interlacements of white ribbon with black border.
Interestingly, though as a book, it is filled with innumerable motifs, borders, and flourishes, and there is absolutely no repetition. No pattern is a copy of another. Those monks knew a thing or two.