Deep inside the massive walls of the old citadel lie a network of tunnels, gun emplacements and ammunition lifts, all aimed at protecting the Verne from attack. Today they lie blinded, the holes though which the guns fired bricked up. It took me a while to work out why all the floors slope gently outwards: to let the guns roll back downhill into their resting positions after recoiling from being fired. It seems that each gun would also have been chained to a iron ring in the ceiling to help contain its recoil. Impressive to see with what care and skill the stone for the arches had been fashioned. No rushed job this: the masonry would not be out of place in a cathedral. And all this prisoner effort; all this material moved, shaped, placed; all this ingenuity, and never a shot fired in anger. Many thanks James for showing me around today: quite an eye opener.