Many books currently being published are large, glossy annuals of the coffee table variety. They tend to highlight the Cathare "country" rather than the history of the people and their persecution and are very much geared towards English speakers.
There are a couple of notable books, for me, that do tell the story of the Cathares plight...
The Yellow Cross, the story of the last Cathares 1290-1329 by René Weis. In depth and in English!. I found it quite heavy going to start with and it took 3 bites to actually get into it. The Cathares were forced to wear the Yellow Cross, a symbol of outcasts throughout history!
Bélibaste by Henri Gougaud. In French. This is a novel but a well told one and the story of a real person. Guillaume Bélibaste was the last of the Cathare Parfaits (the perfects, priests of their religion). He clandestinely traversed the region, blessing the ever diminishing flock of Cathare believer's.
For lighter reading Kate Mosse's trilogy - Labyrinth, Sepulchre and Citadel spans the centuries and is delightful storytelling from the fall of Carcassonne in the 1200's to present day.
We have visited many of the true Cathare sights and learned a lot from those and the guides that oversee them. As I said previously, not all Cathare sites are actually anything to do with the people or the religion they just happen to be of the epoch and in the region.
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@Beachgirl @T Rex I believe munter has it's origins in Scotland. A word I've known my whole life but was never allowed to utter in front of my mother!