11th century–1231

The Cathars (Albigensians), the Albigensian Crusade, and the Founding of the Papal Inquisition

From the 11th century a dualist Cathar teaching spread across southern France. It apparently descended from the Bulgarian Bogomils (mid-10th century, Patriarch Theophylact, the priest Cosmas). It held that two eternal principles exist and that the world was created by the evil one. Liberation came through ascent to the rank of the "perfect". A set of fourteen anathemas from the late 11th century, transmitted under the name of Euthymius Zigabenus, condemned this teaching.

After the murder of a papal legate, Innocent III in 1209 proclaimed a crusade against the Albigensians, named for the town of Albi. It led to a massacre of the population of southern France that continued until 1228–1229. Dominic chose a different path to combat heresy – preaching and asceticism. In doing so he founded the Dominican order.

In 1231 Pope Gregory IX established the papal inquisition. These were tribunals of "inquisitors of heretical depravity", mostly Dominicans. Those they condemned were handed over to the "secular arm". Over time the inquisition became a chief obstacle to freedom of thought in the West.