There are some amazing castles in the Dordogne region of France and Commarques, is one of the most fascinating. It is tucked away in a forest in the Dordogne, and may the Good Lord have mercy on any tourist bus which tries to negotiate the narrow twisty lanes which lead there. Sited deep within the forest of the Vezere Valley, it lies well off the tourist track. Given the roads there, I was pleased I was driving a Fiat 500 - the tiniest car in Christendom. Abandoned since the sixteenth century, Commarques is being lovingly restored, having been used for years as a stone quarry. The earliest habitation was in the caves of the cliffs both below the present castle and amid the wild daffodils of the valley opposite. 

I suspect the valley floor was a good deal more marshy in previous centuries. The earliest defenders merely hauled up the wooden ladder and the sheer six metre limestone cliff was enough to deter the opposition. Mind you, as the fallen block in the first photo below indicates, limestone is not always reliable!

 The later castle was built over the top, fortunately not destroying the earliest inhabited parts.

Flat stones are laid so they shed water outwards. Stone shelters on the French Causses have been roofed like this for thousands of years. The roof is watertight and lasts for hundreds of years. I have seen a similar method used in West Wales on megalithic cliff shelters. 

Castle walls became thinner towards the top. Any rising ground near the castle could be used to achieve a high enough trajectory to keep thumping the stonework at this weaker area. Given sufficient time, there was a chance of causing a breach. 
In the hundred years war, Chateau Beynac, which can be seen beyond the river on the cliffs, was in French hands. Castelnaud was English. At the time of Richard Coeur de Lion, Beynac was his - Aquitainian.