Strimban Who?
Here's a weird one. The style of the cover really reflects the date of publication - this edition is from 1958 - rather than the content or milieu of the novel, which was written a century earlier. Very strange choice, but the illustration is interesting enough on its own.
Don't know who the "Strimban" is who seems to be credited with making the cover, though a web search brought up the names Robert and Jack Strimban... who have a few joint-credits on SF magazine covers and children's books, though, oddly, the same search found a Robert Strimban who is now a sculptor and a Jack Strimban who is an Op artist. If they're the same artists who created this cover, and the pulp covers, and the kids' books - what a bizarre career.
Update! Just found another cover by this mysterious illustrator, and I like it even more. This is also from 1958... perhaps he created a slew of covers for a series of historical fiction? At any rate, if anyone has any info about this fellow, please let me know.