Biphasic Sleep Before the Industrial Revolution

If you have ever woken up in the middle of the night, stared at the ceiling for an hour, and worried that your sleep is broken, you are not alone. Many modern adults panic when they stir at 2 a.m., assuming something is wrong. But historical records and recent sleep science suggest that this natural wakeful period was once considered completely normal—even healthy. Before the Industrial Revolution transformed our relationship with light and time, most people practiced a biphasic sleep pattern, also known as “first sleep” and “second sleep.” Understanding this ancestral sleeping pattern can help you rethink what optimal rest looks like and why your body might be trying to tell you something important.

For centuries, biphasic sleep was the standard. Without artificial lighting, humans relied on the sun and firelight to structure their days. Nightfall meant darkness for twelve or more hours, especially in winter. People did not simply go to sleep and stay asleep until dawn. Instead, they went to bed shortly after sunset, slept for roughly four hours, then woke up for one to three hours of quiet activity. This interval was called “the watch” or “the waking period.” After that, they returned to sleep for another four hours until sunrise. This two-part sleep cycle is documented in medical texts, court records, literature, and personal diaries from Europe, the Middle East, and the Americas. Chaucer’s Canterbury Tales, written in the 1300s, refers to “first sleep” and “second sleep” as a common experience. Historian Roger Ekirch’s landmark research uncovered hundreds of references to this pattern in pre-industrial societies.

What did people do during that wakeful interval? They did not scroll through their phones. They stayed in bed, talked quietly with partners, prayed, reflected on dreams, enjoyed sex, or even did light chores by candlelight. Some used the time to visit neighbors, smoke a pipe, or read by firelight. This period was considered peaceful and restorative—not a sign of insomnia. The science behind biphasic sleep tells us that our bodies may still be wired for this ancient rhythm.

Your sleep architecture naturally cycles through stages of light sleep, deep sleep, and REM sleep in roughly 90-minute intervals. After about four hours of sleep, your brain has completed several cycles and emerges into a lighter stage. This is the moment when you become more sensitive to external stimuli or internal thoughts. In a pre-industrial setting, this natural arousal was simply the signal to begin the watch. Light from a candle or embers kept your circadian rhythm aligned with nighttime, and the darkness before dawn prompted a return to sleep. Today, modern light from street lamps, phone screens, and tablets disrupts this delicate timing. When you wake at 3 a.m. and see a bright blue glow from your phone, your brain interprets it as daylight and suppresses melatonin, making it harder to fall back asleep. That hormonal hijack turns a normal waking period into a frustrating struggle.

Research on biphasic sleep also challenges the widespread belief that eight hours of uninterrupted sleep is the only healthy goal. Some people thrive on a single block of sleep, but many others experience natural awakenings that are not pathological. Sleep scientist Thomas Wehr conducted a landmark study in the 1990s. He had volunteers live in total darkness for 14 hours each night. Within weeks, most participants spontaneously shifted into a biphasic pattern: they slept four hours, woke for one to three hours of calm wakefulness, then slept again. Their mood, alertness, and mental clarity reportedly improved. This suggests that biphasic sleep may be a default human pattern, not a disorder.

The shift to monophasic sleep—one eight-hour chunk—happened during the Industrial Revolution. Factories, streetlights, and later electric bulbs changed night into a workable extension of day. Employers demanded uninterrupted labor shifts, and sleeping in two segments became inconvenient. By the late 1800s, doctors began labeling the wakeful period as insomnia, and the cultural memory of biphasic sleep faded.

For the modern adult, this knowledge offers a liberating perspective. If you wake in the middle of the night, your first step should not be to check your phone or turn on the TV. Instead, try a gentle return to ancestral habits. Lie still, breathe slowly, and let your mind wander. You can read a physical book by warm light, pray, or simply listen to your breathing. Avoid bright light and stressful mental tasks. This quiet interval may be your body’s natural window for reflection and resetting. You might find that you fall back asleep more easily and wake feeling more refreshed.

Biphasic sleep is not a rigid prescription for everyone, but it is a powerful reminder that your sleep is not broken just because it is not continuous. The science of sleep reveals that human rest is more flexible and adaptive than our modern schedules allow. By honoring your body’s ancient rhythms, you can reduce anxiety about wakefulness and rediscover a forgotten form of rest that worked for thousands of years.