I enjoyed the intelligent device of using various voices through fictional letters, notes, etc, to unfold the story. Nicely characterised voices and I couldn't fault the prose (a lovely change!). It wouldn't appeal to those looking for an historical romance. Nor to people who find it a chore to keep up with travelling back and forth in time periods while they're reading.
No knowledge of the history of those times is required in order to enjoy the life and times of this most significant Roman emperor but some care must be taken in noting the dating of the various communications which travel backwards and forwards in time. This structure is intended to exercise the reader and provide a number of ah-ha moments of relishment.