I commented on this great Catholic novel in some of my "lost entries." It’s quite an obscure work, although occasionally a used copy may show up on Amazon.com or bookfinder.com (at present, I see 7 copies available there).
The novel was often compared to Ben Hur. In this case, the novel deals with Roman gentiles for the most part, rather than Jews, and tells a story from the time of Christ with a number of familiar characters–particularly in Roman government. Dion is Dionysius the Areopagite, who receives a mention in St. Paul’s letters.
There are some great scenes in the book of daring adventure. The end seemed a bit rushed to me, trying to tie up loose ends too quickly. While most of the book is carefully researched, the end doesn’t seem to work quite as well. Nonetheless, the overall story is worth the read.
An abridged form of the book can be read online, but it isn’t exactly reader-friendly. A collection of books and journals online called Making of America from the University of Michigan has the book from the magazine Catholic World in serial form, but you have to go to each issue and view the pages. If you search for the title "Dion and the Sibyls" on the page linked to above, you pull up a number of articles that refer to it. The Catholic World articles that are part of it are the ones to look at. It’s best to just get the Journal articles (on the left side of the screen you can click a reference to the journal articles only). Searches for such things as "Lourdes" or "Holy Father" will net many articles from Catholic World also. This is quite a service the U. of Michigan has provided for those who want to read a Catholic magainze from the 1800s.