Black rock outcropping along the road to Rennes-les-Bains coming from Coustaussa. The ancient silver and copper mines in this mountain top, opposite Blanchefort is dubbed ‘le Roc Noir’ (Black Rock). The location allegedly held the treasure chambers of the Visigoth Kings. Pierre Plantard claimed the secrets of the Priory of Sion were hidden here in a Celtic Sanctuary called The Round Temple of the Rocher Noir (Black Rock). Plantard bought 8 plots of land here in the 50s and 60s that were passed on to his son Thomas after his death.
Have been searching the surroundings nearby Roc Negre. There are no mines or a ,¨Temple Rond,¨ as shown on the P.S. map whatsoever.
If you read French, you might find these extracts from the Claude Palmeti and Lena Mirlova book Rennes-le-Château, une autre approche de l’énigme interesting reading material. They have done a lot of research into the old mines of the region.
Cheers!