One With the Darkness by Susan Squires is about a time-traveling vampire who moves between the Italian Renaissance and the Roman Empire. Seriously.
Excess piled on extravagance piled on improbability. I just don't even know what to say. Except that in some odd way, it worked. If you can let yourself go, and forget that the combination is ridiculous, it's a fun read.
Did I mention that Da Vinci built the time machine?