Gothic Architecture. The early semicircular or barrel vaults were found to require extremely massive walls to resist their thrust ; and the first modification was the introduction of transverse arches, thrown across here and there beneath the barrel vaults, to concentrate the chief thrust on certain points, opposite to which buttresses were placed. In the side- aisles, the spaces to be covered being small, the Roman intersecting vaults were used ; but as barrel vaults were ne- cessarily dark and gloomy, it became desirable to introduce l ofty windows t() light tho vaulting, especially of the nave. This could only be pro- vided for by the introduction of cross-vaults, piercing the principal one. It was in struggling with the difficul- ties which attended the use of such cross-vaults on a large scale that the pointed arch was first introduced. Pointed arches are capable of being applied to vaulting bays of any size or shape, as they can be made of equal height what- ever their span. The groins (i. e. intersecting lines of the vaults) were strengthened with ribs, and these ribs and their mouldings became more and more numerous, as the Gothic style developed itself, until the whole vault was covered with them, finally pro- Fig. 43.— Plan of a Gothic Cathedral. Amiens.
