We thought we knew the secrets of Europe's bog bodies. We didn't.

Marshes, mires, and swamps are murky, mysterious places found across northern Europe. A space between two worlds, a bog occurs where dry land and a body of water intersect, creating a soft, spongy terrain that is neither wholly liquid nor solid. This liminal quality may have led the early peoples of northern Europe to associate bogs with the supernatural. They were portals to other worlds, where gods and restless spirits dwelled. In more recent times, peat bogs are seen as valuable natural resources, yet they’ve retained their mystical qualities thanks to the thousands of human bodies that have emerged from their depths.

Europe’s bog bodies have fascinated people since one was first documented in 1640 in Holstein, Germany. Since then, some 2,000 more bodies have emerged in the wetlands of Ireland, the United Kingdom, Germany, the Netherlands, Poland, Scandinavia, and the Baltic States. A groundbreaking study published in January 2023 in the journal Antiquity estimates that figure is conservative, and the actual number could be much higher.

Bog bodies provide a tangible connection with a remote ancestral past, while also serving as a grim reminder of the harsh daily lives of most people. Looking at the mortal remains—whether the peaceful visage of Tollund Man or the curly hair of Bocksten Man—one cannot help but imagine their lives and ponder the causes of their deaths. Were they the most loathed among their people, or were they sacrificed to please the gods? Whether accidental drownings, executed outlaws, fallen warriors, or human sacrifices, these people’s well-preserved remains are providing fascinating windows into a 7,000-year-old tradition and the cultures who practiced it.

(Reconstructing the face of a 700-year-old murder victim.)

Power of peat

Many bog bodies have disturbingly lifelike appearances thanks to a natural chemistry that prevents the decay of some human tissues. Bogs accumulate a muddy layer called peat, which is made of decaying plants and mosses. Peat has been used for centuries as fuel and fertilizer, but many peatlands are now valued for their role as highly efficient and compact carbon sinks and important parts of the fight against climate change.

Sphagnum moss is a key component of peat and gives northern Europe’s bogs their seemingly magical preservation properties. These northern wetlands are cold, low in oxygen, and very acidic. This environment combined with antibiotic properties of the moss creates a perfect soup for preserving the human body’s calcified and keratinous structures—the bones, teeth, skin, hair, and nails. Sphagnum can leach calcium from bones, making them soft and supple. The sinuous qualities of some of the preserved bodies are because of the bones’ bending to pressure in the bog. The aquatic environment also preserves clothing made of wool or animal skin. Plant-based textiles, like linen, do not fare as well over time.

The 2023 study was the first large-scale overview of well-dated human remains from these bogs and included analysis of more than 250 sites and 1,000 sets of remains. Burials were practiced as far back as 5200 B.C., but they flourished between 1000 B.C. and A.D. 1500, from the Iron Age through the Roman era to medieval times.

Assessing all these remains, the study’s authors categorized them into three groups: “bog mummies” with preserved skin, soft tissue, and hair, like the famous Tollund Man of Denmark; “bog skeletons,” whose bones are all that survived, like many of the oldest bog body finds dating back to the ninth millennium B.C.; and a third “mixed” group composed of partially mummified and skeletal remains.

Varying conditions from bog to bog across the continent created different levels of preservation. Each factor—the bog’s acidity, when a body was submerged after death, the time of year, the presence of insects, and the level of exposure over the years—contributed to a body’s condition upon its discovery and determined which parts would be preserved.

Visions and revisions

Scholars had little to go on in the 19th century when they began exploring in earnest how these bodies ended up in the bogs. There are no written records documenting the rituals and beliefs of preliterate societies in the region, and early scholars pulled information wherever they could find it. Many relied heavily on the writings of Tacitus, a first century A.D. Roman historian, to inform their interpretations of the Iron Age bog sites.

Despite never having been to the northern regions himself, Tacitus wrote Germania around A.D. 98. Relying on secondhand and thirdhand sources, he described the northern peoples and their cultures. The work extols the virtues of the Germanic tribes in order to shame Romans for what Tacitus considered their extravagant behavior at home. In the section where he describes crime and punishment among the Germanic peoples, Tacitus includes approving descriptions of hanging certain criminals while drowning others in the bogs.

(Barbarians fought the Romans along the Danube for 400 years.)

This reliance on Tacitus led to colorful (and somewhat imaginative) explanations for the conditions of each body. Their grotesque limbs, often twisted, and grinning skulls, often fractured, supported the interpretation of bog bodies as disgraced people—adulterers, thieves, and outcasts—supposedly punished with first torture, then execution, and lastly submersion in the bog. Many of these explanations held for decades, inspiring poems, stories, and novels about the sad fates of Europe’s bog people.

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Causes of death

Not surprisingly, bog body research has taken many different turns as technology has developed over the decades. New methods—CT scans, 3D imaging, DNA analysis, and radiocarbon dating, to name a few—are creating a larger and more complex rendering of the lives and deaths of these people. Rather than romantic stories about their deaths, scholars are finding more details, more nuance, and even more mystery.

The 2023 study is reshaping the conversation around the ritual importance of bog bodies. Perhaps the biggest reassessment is the role of violence in each person’s death. So many of the bodies were believed to have died violently, because of the state of their corpses, but the Antiquity study could only conclusively identify the cause of death for 57 individuals: 45 died violently, six died by suicide, and four were accidental drownings.

New research has confirmed violent causes of death for some individuals like Denmark’s Tollund Man, who was hanged. Injuries on other bodies are being revealed as postmortem damage caused by pressures from the bog itself or even by accidental damage during excavation. These broken bones and fractured skulls had been seen as evidence of torture or assault. The correct identification of the cause of these injuries could feel satisfying, but it also invites more questions about the deaths.

As technology advances, scientists will be able to collect more data from these bog bodies, teasing out their centuries-old secrets. But as answers emerge, new questions are sure to follow.