The Massacre of the Cathars at Montsegur. In 1244 a few hundred Cathars held out for 10 months in their mountain fortress against 10,000 soldiers. It was a pretty interesting period in church history. Rome started the Medieval Inquisition in response to the Cathars. And the direct cause of the massacre at Montsegur was the assassination of some Inquisitors at Avignonet by Pierre-Roger de Mirepoix, a dispossessed lord and Cathar who was sort of the main military guy at Montsegur. Although the current ruins on top of Montsegur are from a later period, they are still a striking sight on the granite pog on which they stand. Lots more info about the Cathars here.
Also, here are a few nice pics from a visitor to Montsegur. (a tripod site, if that matters).