Ulysses opens and closes with the serpentine letter S. This has been compared to the figures of serpents in the Book of Kells that have their tails in their mouths (ouroboros): Ulysses is a closed circle, ending where it began. In Finnegans Wake Joyce achieved a similar effect by linking the opening and closing sentences of the book so that the former completes the latter. Joyce was greatly influenced by the Book of Kells. Referring to Edward Sullivan's The Book of Kells (a facsimile of some pages of the manuscript with a commentary), he once told his young Irish friend Arthur Power: "In all the places I have been to, Rome, Zurich, Trieste, I have taken it about with me, and have pored over its workmanship for hours. It is the most purely Irish thing we have, and some of the big initial letters which swing right across a page have the essential character of a chapter of Ulysses.