"Oh - right." Rory understood, sort of, if he didn't think about it too hard. "I've heard of the Roman Empire, yeah," he added, hesitantly - most of what he knew came from junior school History and a few documentaries on Channel 4 - "but you look like you're from later than that?" Holy Roman Empire, that was something different, wasn't it...? Why hadn't he read up on history as well as science? It wasn't like he hadn't known there'd be time travel.