Most scholars agree that the stunningly beautiful illuminated manuscript known as the Book of Kells originated in the waning years of the eighth century in a monastery founded by the Irish missionary Colum Cille (also known as St. Columbanus, c. 521-597) on Iona, a remote island just off the west coast of Scotland. But little else about it is certain.

It may have been conceived to celebrate the second centenary of the saint's death on Iona, and left unfinished when the tranquil...