That's not entirely correct, actually. Before artificial lightning got introduced, people slept in two phases, and woke up in the middle of the night to do things. There were even books that suggested things to do in the time before the two sleeps (besides having sex and praying, that is).

More here: https://en.wikipedia.org/wiki/Segmented_sleep and I apologize for not finding a better source.

Very interesting. I'd have thought exactly the opposite - that without artificial lighting, it would make more sense to sleep off all the dark hours.