 Ribbed vaults came into general use in the 12th century.In ribbed vaults, not only are there ribs spanning the vaulted area transversely, but each vaulted bay has diagonal ribs, following the same course as the groins in a groin vault.However, whereas in a groin vault, the vault itself is the structural member, in a ribbed vault, it is the ribs that are the structural members, and the spaces between them can be filled with lighter, non-structural material.