I like historical romance novels (but not the ones that use time travel as a conceit) for many reasons. The covers, for example, are the best.
I have an ongoing quest as I browse used books-- I'm looking the earliest setting. I don't count the ones with a "faeries" bent because they're usually not pinned to a specific era, but if I saw one with "fae" or whatever that was clearly Pre-Roman Britain, I might make an exception. Viking Ecstasy is my current winner even though it's stupid. He's a Viking (790ce at the earliest) and she's an Ancient Egyptian (343bce at the latest, given the culture the author described).
Before you ask, I don't count Clan of the Cave Bear or its sequels, though I like them very much.
So if you spot anything (even if there's time travel involved) and it takes place before the late 8th century drop me a line!