Prior to that, many people across different continents and cultures followed a biphasic sleep schedule. They went to bed in the evening and slept for a few hours, waking up around midnight. Then, they would stay up for a few hours to eat, tend to their children, or add wood to the fire, before finally falling back asleep for their second sleep phase.

And it goes on to mention this pre-industrial biphasic ‘schedule’ many times throughout the article.