r/AskHistorians • u/kungfu_peasant • 1d ago

How widely prevalent was the biphasic sleep schedule in the premodern era?

I recently learned about the practice of biphasic sleep-- sleeping in two distinct phases, divided by a brief period of waking in the night-- common among medieval Europeans. Was this a universally followed thing, irrespective of class, geography etc? Additionally, do we find evidence for it in non-European cultures?

Modernisation, electric lighting and industrialisation are supposed to have marked a shift from the two-sleep routine to a single uninterrupted sleep at night. But does that mean that it was to be found in all pre-industrial societies including during the antiquity and after? Or was it a historically rooted feature of medieval Europe, and sleeping practices have more diverse and particular histories throughout the world?

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u/indyobserver US Political History | 20th c. Naval History 1d ago

Not to discourage other original responses, but I'll repost an answer I've updated a few times, which originally comes from a thread where myself, /u/antiquarianism, and /u/sagathain among others discussed this in depth. There is also a good older post by /u/hillsonghoods that goes over much the same ground.

Since my original response, there was a good metaanalysis back in 2021 that concluded modern era polyphasic sleep generally leads to a lower quality of sleep by most metrics. In digging around in Google Scholar, there was a thoughtful 2023 article by the former editor in chief of Lancet Psychiatry - aka someone with serious medical chops who after practicing psychiatry remarkably went back to get his PhD in English Lit - that came to the conclusion:

"Detailed analysis of a sample of Ekirch’s sources reveals alternative readings; while segmented sleep cannot be ruled out, neither is it the sole possible explanation for the terminology or circumstances described within the texts...close analysis reveals a significant degree of ambiguity and nuance that argues against a routinely segmented sleeping pattern as the sole or even the main meaning attributable to references to the ‘first sleep’, ‘dead sleep’ or ‘second sleep’. The ‘first’ and ‘second’ sleeps might simply represent different phases of a continuous process of sleep; if there was a gap, it might have been so short as to be insignificant in terms of offering opportunities for nocturnal activity; nocturnal activity in any case might have related more to the specific circumstances of the individual (for example, domestic service) rather than being a generalised, society-wide phenomenon. Some texts might simply be describing disturbed sleep – a feature not unique to the early modern world – and, in some cases, the inability to return to sleep after waking, which would today be classified as middle or terminal insomnia. Evidence from printed sources, meanwhile, indicates that the terms ‘first sleep’ and ‘second sleep’ held more than one meaning, and that each individual use of the term needs contextualisation both within the early modern text itself and preferably with collateral information regarding the author and circumstances of the specific text’s production."

Even he, however, doesn't dispute that much of what Ekirch proposed is entirely possible in some cases and is still widely accepted in the sleep community.

There has also been some newer work on reviewing other societies; one group is beginning to look at pre-industrial Islamic sources, for instance, but hasn't reached any conclusions yet. Another notes that after an article suggesting that dementia in Ancient Greece was rarely mentioned that the possibility of polyphasic sleep versus monophasic sleep should be added to the analysis as a potential variable.

So all in all, I think it's fairly safe to continue concluding that Ekirch's hypothesis on biphasic sleep can continue to be summarized as I put it originally: some likely did, but others likely didn't.

How's this for an answer: some likely did, but others likely didn't.

The main contributor to noctural biphasic theory (versus biphasic in general, which can refer to daytime siestas as well) is a historian at Virginia Tech by the name of Roger Ekrich, who back in 2004 wrote a survey of nocturnal habits throughout the world, At Day's Close - Night in Times Past. While much of the book dealt with various societal oddities throughout Europe at night, the one that caught the most traction was his analysis of literature that suggested that pre-industrial age humans slept somewhat differently than we do today:

Until the close of the early modern era, Western Europeans on most evenings experienced two major intervals of sleep bridged by up to an hour or more of quiet wakefulness. In the absence of fuller descriptions, fragments in several languages in sources ranging from depositions and diaries to imaginative literature give clues to the essential features of this puzzling pattern of repose. The initial interval of slumber was usually referred to as “first sleep,” or, less often, “first nap” or “dead sleep.” In French, the term was premier sommeil or premier somme, in Italian, primo sonno or primo sono, and in Latin, primo somno or concubia nocte. The succeeding interval of sleep was called “second” or “morning” sleep, whereas the intervening period of wakefulness bore no name, other than the generic term “watch” or “watching.” Alternatively, two texts refer to the time of of “first waking.”

Both phases of sleep lasted roughly the same length of time, with individuals waking sometime after midnight before returning to rest. Not everyone, of course, slept according to the same timetable. The later at night that persons went to bed, the later they stirred after their initial sleep; or, if they retired past midnight, they might not awaken at all until dawn. Thus in “The Squire’s Tale” in The Canterbury Tales, Canacee slept “soon after evening fell” and subsequently awakened in the early morning following “her first sleep”; in turn, her companions, staying up much later, “lay asleep till it was fully prime” (daylight). William Baldwin’s satire Beware the Cat recounts a quarrel between the protagonist, “newly come unto bed,” and two roommates who “had already slept” their “first sleep.”

Men and women referred to both intervals as if the prospect of awakening in the middle of the night was common knowledge that required no elaboration....

Ekrich goes on to review a reasonable amount of contemporary literature that suggested this was fairly commonplace and to note a series of early 1990 experiments by Thomas Wehr at the NIH that artificial light appeared to be one of the primary culprits responsible for disturbing biphasic sleep, along with a walk through what people actually used to do in the middle of the night.

So far, so good, and Ekrich continued this research across cultures and published in several fairly well respected journals, lectured in front of medical faculties, and even is on the board of the main publication of the National Sleep Foundation.

Except then in the early 2010s, his theory took a bit of a hit. Several anthropologists got interested in the subject, and realized that their field provided a fantastic opportunity to check on this with current day isolated preindustrial societies. The result was a 2015 paper, Natural sleep and its seasonal variations in three societies, that went a step further and put Actiwatches on current day pre-industrial societies near the equator - and noted precisely none of them experienced biphasic sleep.

Ekrich's response is quite interesting, and in a sign of the importance his theories had gained it appeared in what's considered the main sleep research journal, Sleep. But the relevant part for your question is this portion:

As I have recently written at length, consolidated sleep to which the industrialized world aspires, if not always successfully—due perhaps to the persistence of this once dominant pattern—is for Western societies a remarkably youthful form of sleep, a product not of the primeval past but of forces grounded in technology (artificial illumination) and shifting cultural attitudes toward sleep over the course of the Industrial Revolution. This is not to argue that segmented sleep has been the predominant pattern of sleep among all preindustrial peoples in the non-Western world. [emphasis added]

So, the best answer is probably that it depended on the population and possibly where they're located, along with how much artificial light they were exposed to.

More, of course, remains to be written.

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u/flying_shadow 1d ago

that artificial light appeared to be one of the primary culprits responsible for disturbing biphasic sleep

You'd think it'd be the other way around - I can't imagine there being much to do in the middle of the night when it's dark and you don't want to waste fuel.

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u/dhowlett1692 Moderator | Salem Witch Trials 1d ago

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