This is #4 in a series called "Slaves of the Empire," by Dael Forest. The series was fairly obviously an attempt to capitalize on the Gor phenomenon. The covers are all done by Boris Vallejo, just as most of the Gor covers were.
However, in this case the stories take place in ancient Rome, and most of the five books in the series involve different characters. The sexual situations are also much milder than in the later Gor books, and the slavery is much less demeaning as it is described.
I've been buying the series because several of them were actually written by Kenneth Bulmer, whose work I collect. This particular one I'm pretty sure was written by Ken.