The Splendor of English Gothic Architecture. John Shannon Hendrix

      When the present vaulting was added later, perhaps after the collapse, the walls needed to be shored to support the extra weight. Part of the shoring involved building a second arcade over the first to support the increased wall thickness above, but the builders did not want to conceal the original arcade, so the piers and arches of the second arcade were made to alternate with the piers and arches of the original arcade, resulting in the present syncopated double arcade. The apexes of the arches of the first arcade are also visible through pierced openings in the second arcade. The first arcade is of limestone; the second overlapping arcade is built with Purbeck marble in the south aisle and Alwalton marble in the north aisle. The builders also added additional vaulting shafts to the wall to support the new vault, resulting in the present shafts one on top of the other. The bays of the arcading do not correspond to the bays of the vault as established by the vaulting shafts. Flying buttresses were added to the exterior existing buttresses, and transverse arches were built in the triforium chamber, a method of shoring which was repeated in the nave and Angel Choir, or retrochoir, of the cathedral.