Biphasic sleep: an ancient way of resting

18 July 2025 -

Simmons Brand

Do you wake up in the middle of the night? What if it’s perfectly natural?

Do you often find yourself waking up between sleep cycles? Don’t worry, this isn’t necessarily a sign of a sleep disorder. This phenomenon actually corresponds to an ancient form of rest: biphasic sleep. Unlike the continuous sleep pattern we are familiar with today, this rhythm divides the night into two distinct periods of rest, separated by a waking phase.

Although this type of sleep seems unusual nowadays, research conducted by the historian Roger Ekirch reveals that this habit was once quite common. By studying ancient legal documents, he has highlighted recurring references to the ‘first sleep’ and the ‘second sleep’, found in numerous historical writings. He has thus identified more than 2,000 instances in texts ranging from antiquity to the 19th century, including works by major figures such as Erasmus and Plutarch, as well as in Homer’s The Odyssey. This nocturnal routine, now forgotten, was therefore once deeply ingrained in people’s habits.

Biphasic sleep: a little-known ancient routine

Nowadays, we tend to seek uninterrupted, continuous sleep. Yet this model has by no means always been the norm. In the past, our ancestors followed a pattern ofsegmented sleep, also known as biphasic sleep. They would generally go to bed around 9 or 10 pm, sleep for a few hours, then wake up naturally in the middle of the night for one to two hours before going back to bed to finish their rest.

During this night-time break, it was not uncommon to remain lying in bed, taking advantage of this quiet moment to pray, meditate, or even share moments of intimacy with one’s partner. Some also used the time to carry out a few household chores, look after the children, tend the fire, or reflect on their recent dreams, which were often more vivid in their minds at that time.

This way of resting, although rare today, was deeply ingrained in the daily and social life of the past.

Biphasic sleep in the Middle Ages: between belief and necessity

In the heart of the Middle Ages, an era steeped in mystical traditions and esoteric beliefs, sleep was far from what it is today. Dreams played a central role, often interpreted as divine messages or signs to be pondered. Sleeping positions, too, were dictated by the beliefs of the time: sleeping on one’s back was avoided, as this position evoked death. Conversely, the sitting position was favoured, in accordance with the recommendations of Hippocrates, inherited from antiquity. Sleeping on one’s stomach, meanwhile, was associated with illness.

But if biphasic sleep became the norm, it was also for practical and social reasons. In the 16th century, this nocturnal routine was common among modest families – peasants, labourers or craftsmen – exhausted by gruelling days. Come evening, many lacked the energy for long vigils. After an initial sleep, the short period of wakefulness allowed them to keep watch over the home, tend the fire, or simply maintain a degree of vigilance in a context of widespread insecurity.

The decline of biphasic sleep with the Industrial Revolution

With the dawn of the 19th century and the advances of the Industrial Revolution, lifestyles underwent profound changes – including our sleeping habits. The introduction of stronger security measures, such as the emergence of police forces, gradually alleviated fears of night-time intrusions. This increased sense of security reduced the need to stay awake between sleep cycles.

At the same time, artificial lighting – thanks to the invention of the gas lamp, followed by electricity – radically transformed our evenings. It has now become possible to stay active for longer after nightfall, which is gradually altering the biological clock. Artificial light stimulates wakefulness, disrupting the natural sleep cycle in two stages.

According to the historian Roger Ekirch, it was at this time that segmented sleep began to disappear. The reason: a new social and economic organisation centred on productivity and the regularity of working hours. The notion of performance became dominant, and the rhythms imposed by work dictated continuous and more compact rest periods.

It was also during this period that the first major evening entertainment venues emerged: theatres, music halls, cinemas, cabarets… These evening entertainments contributed to pushing back bedtime, making it even more difficult to maintain a biphasic sleep cycle. Thus, throughout the 19th century, this ancient tradition gradually gave way to monophasic sleep, which has become the norm in our modern societies.

Biphasic sleep: a natural rhythm for humans?

Can biphasic sleep be considered the human body’s original rhythm? To answer this question, the scientist Thomas Wehr conducted an experiment in the early 1990s. He placed 15 volunteers in an environment without artificial light for several weeks, in order to observe how their biological clocks would react to the absence of modern light stimuli. After three weeks, the participants naturally adopted a pattern of two-phase sleep. Their night was split into two: an initial sleep period of 3 to 5 hours, followed by a period of wakefulness lasting around 1 to 2 hours, before falling back into a second cycle of a further 3 to 5 hours. This result suggests that, without external constraints, humans could spontaneously revert to this ancient model. Moreover, certain contemporary communities, notably in Suriname, Nigeria and Madagascar, still maintain similar rest patterns today, with fragmented sleep naturally integrated into their way of life. However, these observations must be treated with caution. Other studies conducted among pre-industrial populations in South America or Africa have not identified biphasic cycles. This suggests that split sleep is not universal, and that its adoption likely depends on numerous factors: environment, culture, climate, lifestyle…

Is fragmented sleep a sign of a disorder?

Waking up in the middle of the night or adopting a biphasic sleep pattern is not necessarily a disorder. Whether you’re tempted to try this age-old pattern or prefer uninterrupted sleep, the key remains the same: giving your body sufficient, restorative rest.

According to the recommendations of Santé publique France, a child needs around 10 hours of sleep, a teenager 9 hours, whilst adults should aim for between 7 and 9 hours a night. However, the reality is quite different: on weekdays, the average sleep duration in France is around 6 hours and 42 minutes, and only 7 hours and 42 minutes at the weekend. This chronic sleep deficit raises real concerns for public health.

If you are feeling the effects of this sleep debt, consider incorporating restorative naps into your daily routine. Similarly, a few simple adjustments – such as adopting a bedtime routine or using products that promote sleep – can greatly improve the quality of your night’s sleep.