Here's something your sleep app won't tell you: for most of human history, nobody slept through the night. Medieval people went to bed at dusk, woke up around midnight, stayed up for an hour or two, then went back to sleep until dawn. They didn't consider this a problem. They had a word for it.

They called it "first sleep" and "second sleep," and it shows up in sources from prayer manuals to court depositions to medical texts. It wasn't a disorder. It wasn't poor sleep hygiene. It was just how humans rested before cheap artificial light convinced us that eight unbroken hours was the only correct way to do it. The medieval pattern might have something to teach us about the bodies we're still walking around in.

Medieval people called it primus somnus — first sleep. It started not long after dark, sometimes as early as eight or nine in the evening. Entire households would bed down together, servants and family alike, often in the same room. This wasn't laziness; it was economics. Candles were expensive, firewood wasn't free, and once the sun disappeared there wasn't much productive work you could do anyway.

But there was a biological logic underneath the practical one. Sleep researchers, most notably Roger Ekirch at Virginia Tech, found that when modern subjects are placed in environments without artificial light for extended periods, they naturally drift into a biphasic pattern — falling asleep, waking after about four hours, then sleeping again. Their bodies chose the medieval schedule once the LED screens and overhead lighting disappeared. The first sleep phase appears to be dominated by deep, slow-wave sleep, the kind your body uses for physical repair and immune function.

So medieval people weren't struggling through a broken night. They were getting a concentrated dose of the most restorative sleep phase first, while their bodies were freshest and the day's physical labor demanded recovery. First sleep was the heavy lifting of rest. Everything after it was a bonus.

Takeaway

The medieval first sleep wasn't a flawed version of modern sleep — it may have been the default human pattern. When we removed darkness from our lives, we didn't improve sleep; we just forgot what it originally looked like.

The wakeful period between first and second sleep — sometimes called the watch — lasted roughly one to two hours. And far from being a groggy inconvenience, medieval sources describe it as a uniquely calm and productive time. People prayed, talked with their bedfellows, had sex (doctors actually recommended the interval for conception, arguing the body was relaxed and the timing ideal), smoked tobacco in later centuries, or simply lay in the dark and thought.

Monastic communities built this interval directly into their schedules. The office of Matins, one of the canonical hours of prayer, was deliberately set in the deep middle of the night. Monks rose, filed into cold churches, chanted psalms, and returned to bed. It wasn't punishment — it was architecture around a biological reality. The Church didn't invent the waking period; it made use of one that already existed. Court records also reveal that the watch was when neighbors visited, petty crimes were committed, and — according to more than a few depositions — when people overheard things they probably shouldn't have.

What's striking is the emotional quality people attributed to this interval. Writers described it as a time of unusual clarity and intimacy, a liminal space between the demands of the day. Modern sleep science has a possible explanation: subjects who wake naturally between sleep cycles show elevated levels of prolactin, a hormone associated with feelings of calm and contentment. The medieval midnight wasn't anxious wakefulness. It was something closer to meditation.

Takeaway

If you wake at 2 a.m. and can't get back to sleep, you might not have insomnia — you might be experiencing an ancient pattern your body still remembers. The anxiety about being awake may be worse than the waking itself.

Second sleep — secundus somnus — picked up where the watch left off and carried people through to dawn. Sleep researchers note that this phase tends to be rich in REM sleep, the stage associated with dreaming, memory consolidation, and emotional processing. If first sleep repaired the body, second sleep organized the mind. Medieval dream interpretation manuals, which were wildly popular, may have flourished precisely because people regularly woke from a REM-heavy phase with vivid dreams still fresh.

So what killed biphasic sleep? In a word: light. The spread of affordable street lighting in the late seventeenth century, followed by gas lamps and eventually electricity, gradually pushed bedtimes later. If you could read, work, or socialize after dark, there was no reason to go to bed at nine. The first sleep crept later and later until it merged with the second. By the early twentieth century, references to "first sleep" had vanished from common English. The Industrial Revolution's factory schedules finished the job — rigid work hours demanded a single consolidated block of rest, and the biphasic pattern was reframed as a medical problem.

The language tells the story. In 1700, "first sleep" appeared in English texts without explanation because everyone knew what it meant. By 1900, the phrase required a footnote. We didn't just change how we slept — we forgot we had ever slept differently. And then we started diagnosing the old pattern as a disorder.

Takeaway

Consolidated eight-hour sleep is a modern invention, not a biological law. Many people who struggle with middle-of-the-night waking may be fighting their own physiology rather than suffering from a malfunction.

Medieval people weren't sleep-deprived sufferers waiting for someone to invent the mattress store. They had a rhythm that worked with darkness rather than against it, and their bodies did things in two stages that we now try to cram into one.

You probably can't — and maybe shouldn't — fully reconstruct a medieval sleep schedule in a world of electric light and alarm clocks. But the next time you find yourself awake at two in the morning, staring at the ceiling with growing panic, consider this: your great-great-great-grandparents would have just called it Tuesday.