Richard Phené Spiers, 1911 Encyclopædia Britannica (1911)
“ VAULT [1] (Fr. voute, Ital. volta, Ger. Gavolbe) , in architecture, the term given to the covering over of a space with stone or brick in arched form, the component parts of which exert a thrust and necessitate a counter resistance. In the case of vaults built under the level of the ground, the latter gave all that was required, but, when raised aloft, various expedients had to be employed, such as great thickness of walls in the case of barrel or continuous vaults, and cross walls or buttresses when intersecting vaults were employed. ”
