# The keystones of Notre-Dame Cathedral

The term "keystone" describes the function of this stone element that locks the ribs of the vault at its summit. The keystones of Notre-Dame typically take the form of a disk toward which the ends of the ribs converge.

These three keystones digitized here by PLEMO3D come respectively from the high vault of the nave, from the extreme bay of the south arm of the transept, and from a chapel of the nave.