Some other reviews led me to believe I was going to hate this and deride it mercilessly for being utter crap, but I don't and won't. I kind of loved it, and I'll tell you why.
It's not because of the historical accuracy. That obviously wasn't a concern here. The story was based on one image, and focused on what might have happened to achieve a moment like that. This is a highly stylized, highly fetishized, highly modern-opinion-ized version of Rome.
It wasn't because the heroine was likeable, because she wasn't. There's not anything likeable about her at all, really, except maybe her perseverance. But she's interesting. I'm not asked to like her, only to understand her.
It was because this is a really great pulp action novel. Blood, sex, violence, exotic locations, intrigue. The writing flows well and isn't too stylized or self-aware, and it's no chore to read. It's not a timeless work of literature or one of my favorite books, but it'll only take one afternoon to read. Embrace the glorious VIGOR of it, the intensity that's so serious as to be a bit silly. It's liberating. It's the perfect vacation book, whether you're on vacation or not. A bucket of popcorn wouldn't be amiss, either.
It sort of reminded me of Mara, Daughter of the Nile... Mara is a cut above, though, better history and focused on absolutely delicious intrigue.