The Medieval inquisition: scale-free networks and the suppression of heresy

Qualitative evidence suggests that heresy within the medieval Church had many of the characteristics of a scale-free network. From the perspective of the Church, heresy can be seen as an infectious disease. The disease persisted for long periods of time, breaking out again even when the Church believed it to have been eradicated. A principal mechanism of heresy was through a small number of individuals with very large numbers of social contacts. Initial attempts by the inquisition to suppress heresy by general persecution, or even mass slaughter, of populations thought to harbour the ‘disease’ failed. Gradually, however, inquisitors learned about the nature of the social networks by which heresy both spread and persisted. Eventually, a policy of targeting key individuals was implemented, which proved to be much more successful.