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Building a Castle: Rib Vaults

The castle towers, especially circular or polygonal towers, could have magnificent vaulted ceilings, particularly in the lord’s chambers. Later builders devised methods for long vaulted ceilings in churches. At Guédelon the great tower has a cross-rib vault which required skill to create.

Notre Dame de Paris

Master mason Florian Renucci and his teams of masons and carpenters achieved one of their greatest feats in planning, carving, constructing and fitting the the cross-rib vault. And remember, part of the brief in building Guédelon was to use only the tools and methods used in medieval times.

The first stage is to build a wooden frame on which the stones rest while the roof is being constructed. When building an arch, the keystone is the last block to be placed, which holds the arch in place. In a rib vault, it is the first stone. The beautifully carved keystone is lifted into place and acts as a guide for building the ribs on top of the wooden frame.

Moving and hoisting the keystone into place is a very difficult manoeuvre. It’s carving is fragile and can easily be damaged if it is knocked or mishandled. With the keystone in place, the ribs of the vault can be constructed. The testing moment comes when the wooden frame is removed and lowered to the floor to be dismantled. Will the ribs take the weight? 

Bethanie Chapel Hong Kong

In Guédelon each of the six ribs bore a load of about 25 tons. At the end of each rib, a long springer stone deeply embedded in the rubble core carried the weight into the walls.

[adapted from The Medieval Castle Haynes Manual by Charles Phillips]

Ann Marie Thomas is the author of four medieval history books, a surprisingly cheerful poetry collection about her 2010 stroke, and the science fiction series Flight of the Kestrel. Book one, Intruders, and book two Alien Secrets, are out now. Follow her at