Explanations for why the bog victims were killed have included accident, punishment for crimes, execution of prisoners, and robberies gone wrong. In her new book, Bog Bodies Uncovered, Miranda Aldhouse-Green, a British archaeologist and expert on Celtic antiquity, argues that none of these causes make sense of all the available evidence. Bringing together results from forensic examination of the bodies with the testimony of classical authors and material gathered by ‘dry land’ archaeologists, she suggests that the likeliest explanation is also among the most disturbing: that they were victims of human sacrifice, and were left in the waters of the bog as an offering to the gods.

The first thing everyone remarks on when confronted with one of the bog bodies is their remarkable state of preservation. The Tollund Man, perhaps the most famous bog body, has been called the “perfect corpse,” chiefly because of the exquisite condition of his face and head. Discovered in 1950 by peat cutters in a Danish bog, he was buried naked, save for a skin cap and leather belt. He had been hung, and the noose that was used was still around his neck. Given the violence he seemed to have suffered before death, it always comes as a surprise that his face is the picture of calm. The Danish archaeologist P.V. Glob, present on the day after he was unearthed, described him as having “a gentle expression—the eyes lightly closed, the lips softly pursed, as if in silent prayer.”

The Tollund Man’s preservation is awe-inspiring, but it wasn’t deliberate. Unlike Egyptian mummies, the bog bodies owe their state to an accident of chemistry. The bogs in which they were buried contain little oxygen, which helps to inhibit bacterial growth. The most important ingredient for the bog bodies’ survival though comes from a plant called sphagnum. When sphagnum dies, it releases polysaccharides which block bacterial metabolisms. This helps keep organic matter like skin, wood, fur, and textiles from succumbing to decay.

Bogs cure bodies in a process akin to tanning, but while they are wonderful at preserving skin, they eat away at bones, leaving the bodies’ skeletons shrunken and sometimes, completely absent. At the same time, acids in bog water destroy DNA, making genetic studies impossible. Most bog bodies have been discovered in the process of excavating peat for use as fuel, and as a result, many have been hacked apart by spades and shovels, and more recently, by mechanical peat excavators. (The poor Grauballe Man even had his head stepped on, leaving it badly deformed). Modern forensic specialists have had to work hard to distinguish trauma inflicted on the bodies in life from the damage done to them when they were found.

On top of post-mortem trauma, the unusual preservation of the bog bodies can pose an additional challenge to investigators. When a body was found in the Lindow Moss in 1983, police at first thought it belonged to a recently murdered woman. By coincidence, it was found just a thousand feet from the cottage of a man who was suspected in his wife’s disappearance. Confronted with the body, he admitted to the crime. Only a few months later did it become apparent that the body was that of a two-thousand year old man.