Vault (architecture)

A Vault (French. voute, Italian. volta, German. Gewölbe, Polish. sklepienie) is an  architectural term for an arched form used to provide a space with a ceiling or roof. The parts of a vault exert a thrust that require a counter resistance. When vaults are built underground, the ground gives all the resistance required. However, when the vault is built above ground, various replacements are employed to supply the needed resistance. An example are the thicker walls used in the case of barrel or continuous vaults.  Buttresses are used to supply resistance when intersecting vaults are employed.
See more at Wikipedia.org...