The sudden emergence of witch trials in early modern Europe may have been fueled by one of humanity’s most significant intellectual milestones: the invention of the printing press in 1450.

A recent study in Theory and Society shows that the printing of witch-hunting manuals, particularly the Malleus maleficarum in 1487, played a crucial role in spreading persecution across Europe. The study also highlights how trials in one city influenced others. This social influence — observing what neighbors were doing — played a key role in whether a city would adopt witch trials.

“Cities weren’t making these decisions in isolation,” said Kerice Doten-Snitker, a Complexity Postdoctoral Fellow at the Santa Fe Institute and lead author of the study. “They were watching what their neighbors were doing and learning from those examples. The combination of new ideas from books and the influence of nearby trials created the perfect conditions for these persecutions to spread.”

The witch hunts in Central Europe took off in the late 15th century and lasted for almost 300 years, resulting in the prosecution of roughly 90,000 people, with nearly 45,000 executions. Belief in witches and witchcraft had been present in European culture for centuries, but the level of systematic, widespread persecution that occurred during this period was unprecedented.

According to Doten-Snitker, the advent of the printing press allowed for the rapid dissemination of ideas about witchcraft that had previously been confined to small intellectual circles, such as religious scholars and local inquisitors. The most infamous of these publications, the Malleus maleficarum, was both a theoretical and practical guide for identifying, interrogating, and prosecuting witches. Doten-Snitker explains that once these manuals entered circulation, they provided a framework for how local authorities could manage suspected witchcraft in their communities.

For their study, Doten-Snitker and colleagues build on previous research by looking beyond broad economic and environmental factors and focusing on how new ideas about witchcraft spread through social and trade networks, influencing behaviors in a slow but powerful way.

They analyzed data on the timing of witch trials and the publication of witch-hunting manuals from 553 cities in Central Europe between 1400 and 1679, when there was a noticeable reduction in both the frequency and intensity of persecutions. Their findings suggest that the publication of each new edition of the Malleus maleficarum was followed by an increase in witch trials. However, it wasn’t just proximity to a printing press that determined whether a city would conduct trials; the influence of neighboring cities played an equally important role.

As one city adopted the practices outlined in the Malleus maleficarum, nearby cities often followed suit, learning from each other’s actions. This process, which Doten-Snitker and her coauthors term ideational diffusion, often took many years as people in towns and cities needed time to digest new ideas about witchcraft and turn them into behavior. However, once it took hold it created a slow but powerful ripple effect that percolated across the continent.

Though the research focuses on historical witch trials, Doten-Snitker sees clear modern parallels on how large-scale social change occurs.

“The process of adopting witch trials is not unlike how modern governments adopt new policies today,” Doten-Snitker said. “It often starts with a change in ideas, which are reinforced through social networks. Over time, these ideas take root and change the behavior of entire societies.”