...Les claveaux, dans l'architecture du moyen âge, étant toujours intradossés et extradossés, sauf de très-rares exceptions, il en résulte que les claveaux d'un même arc sont tous de même forme et de même dimension, ainsi que le démontre la fig. 1. A sont les sommiers, B la clef et C les claveaux...

This image comes from Dictionary of French Architecture from 11th to 16th Century (1856) by Eugène Viollet-le-Duc (1814-1879).

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