Since reading books on Early Christianity and gnosticism, it made me curious to learn more about the inquisition. The best book I’ve read of many is A History of the Inquisition of the Middle Ages by Henry Charles Lea. It is very long but extremely fascinating.
There is this myth that people who were midwives or practiced Wicca were burned, but it was for the most part peaceful Gnostic groups (the first volume), which this book discusses many of the different Gnostic groups and their beliefs (Cathars, Valentinians, Waldensians, etc.). Later volumes discuss the persecution of the Templars, the spiritual Franciscans, other groups, and the use of the inquisition to achieve political aims and power.
I was shocked to learn that many current new age beliefs existed during the inquisition but were quieted in the name of “heresy.” Some torture techniques to elicit confessions or to stimulate conversions were horrifying (this book is mostly written from historical transcripts which the Catholic Church kept records of its activities during the inquisition).
The Malleus Malificarum (aka the Hammer of Witches) is a treatise written on witchcraft that endorsed the extermination of witches. It described how to best torture them to elicit confessions. It was a best seller, selling close to the bible, at its time and affected culture. It was a hard read but I think important to understand the Christian mindset at that time (which there are some remnants of these beliefs today).