The Book of Kells is an illuminated manuscript Gospel book in Latin, containing the four Gospels of the New Testament together with various prefatory texts and tables. It was created by Celtic monks ca. 800 or slightly earlier.  It is a masterwork of Western calligraphy and represents the pinnacle of Insular illumination. It is also widely regarded as Ireland's finest national treasure.
The illustrations and ornamentation of the Book of Kells surpass that of other Insular Gospel books in extravagance and complexity. The decoration combines traditional Christian iconography with the ornate swirling motifs typical of Insular art. Figures of humans, animals and mythical beasts, together with Celtic knots and interlacing patterns in vibrant colours, enliven the manuscript's pages. 
SOURCE: Wikipedia

Compare this page of the the book of Matthew in the Lindisfarne Gospels.