Good question and a great segue into a fun fact: it seems quite possible people waking up in the middle of the night was the norm for centuries, and that the assumption of sleeping the whole night is potentially a more modern idea.

I am having trouble finding a specific article, but a historian recently catalogued a large number of historical entries which note ‘the second sleep’. He basically posited that it’s likely that for ages, people in the pre-industrial world would sleep for about 3-4 hours, wake up in the middle of the night for an hour or two, and would then go back to sleep. Article talking about it.

Articles quite often say that writing as far back as homer talk about an hour which terminates the first sleep like a normal thing everyone knows about. I haven’t read much of homer or Virgil so i can’t personally confirm or deny that.