Every now and then, archaeologists find the remains of somebody buried in an unusual manner for the time period and culture they lived in. Known as "deviant burials," they range from decapitated bodies to strange body positions, and even "live burials".

Reasons for unusual burials range too. Some are punishment for criminals; live burials were once used as a method of execution in England for such crimes as "those who have dealings with Jews or Jewesses, those who commit bestiality, and sodomists". Others, where bones have been deliberately broken or a stake placed through their heart, have taken place out of fear that the dead may return in some way.

A new study in the journal PLOS ONE has looked at a particular type of deviant burial that became more frequent during the Middle Ages through to the Early Modern period in German-speaking Europe: placing bodies face down in their graves.

In the research, anthropologists from the Bern University’s Institute of Forensic Medicine in Switzerland studied 95 prone burials from 60 archaeological sites in Switzerland, Germany, and Austria, analyzing them in terms of geographical distribution, dating, burial features, body position, age-at-death, and sex. They found that as time went on, there was a shift in the way prone burials took place, and the reasons behind the burials themselves.

During the Middle Ages, the team found, some of the remains had likely been buried in this unusual position at the request of the deceased. Some were found with signs of wealth, or in favorable places within churchyards or chapels, suggesting that they were placed face down as a sign of humility before God. King of the Franks, Pepin the Short – father of the much more famous Charlemagne – was one of the most powerful rulers of his time, yet chose to be buried face down as a way of atoning for his (even less famous) father's sins.

Later on in the Middle Ages and in the Early Modern period, around the 1300s and 1400s, the team found that prone burials began to increase, and as they did, they took place further away from favorable burial grounds, though still within consecrated grounds. The authors write that while prone burials could indicate punishment, the fact that they took place in graveyards suggests that this wasn't the case, or their sins weren't enough to deny a churchyard burial. 

Instead, they note that the increase coincided with the popularity of tales of the revenant, or the undead, particularly the German folklore of the nachzehrer, a sort of vampire. Nachzehrer were believed to be the dead that lived off themselves and others.

"The Nachzehrer devour their own bodies, including their funeral shrouds, and in doing so, cause smacking sounds," the authors write in the paper. "They are also associated with epidemic sickness; whenever a group dies from the same disease, the person who dies first is labeled to be the cause of the group's death." 

Around this time, between the 14th and 17th centuries, the plague and other diseases swept through Europe. The team believes that the increase in disease epidemics may explain the increase in prone burials, as people began to see more of the process of decomposition while they were overwhelmed with bodies, increasing their fear of the dead.

"The rapid spread of epidemic diseases in the Late Middle Ages, namely plague, and later also of typhoid fever, syphilis, and cholera, promoted the fear of the dead, not only in the sense that people were afraid of infection, but also because of an intensified dealing with corpses. The perception of reanimated corpses was surely influenced by the experience of decomposing, moving, and smacking bodies," the authors write.

During the height of the plague, they found few examples of people being buried face down, which they say could indicate that the position was used as a superstitious attempt to stop an outbreak.

"The fact that prone position is lacking from attested, plague row burial sites (mass graves not included) could be indicative of prone burials dating to the early or late phases of the epidemic during which otherwise normal burial practices were kept but the disease was feared the most. Prone position could therefore represent an act to protect the living by restraining the dangerous dead from returning and the disease from spreading."

Other reasons for prone burial are still possible, and the team told National Geographic they want to investigate further by analyzing the DNA of people buried in this way, to see if they show signs of the plague, or else reveal other clues that might offer up an alternative explanation.