Most visitors to Trinity College Dublin's Old Library come to see the Book of Kells, but the case beside it holds an older and, to specialists, arguably more important book. The Book of Durrow was made a full century or more before Kells, somewhere in the second half of the seventh century, and it is the earliest Insular gospel book to survive with its full program of decoration intact: six carpet pages of pure geometric and interlace ornament, and framed pages introducing each gospel with the symbolic beast assigned to its evangelist, a lion, an eagle, a calf, a man. Nothing earlier in Western manuscript art combines those elements this way, which is exactly why the book matters more than its comparative plainness beside Kells might suggest. Kells inherited a visual language Durrow was still inventing.
Durrow's text is workmanlike where Kells is showy, a mixed Vulgate and Old Latin gospel text copied without the flourishes that make Kells's individual letters into art in their own right. That difference in ambition is part of what lets scholars place Durrow first: later Insular manuscripts elaborate on ideas Durrow states plainly, rather than the reverse. The book stayed at Durrow Abbey in Ireland for most of a thousand years before a seventeenth century bishop brought it, along with Kells, to the library where both still sit today.