Duke Robert Guiscard (the Norman Robert d'Hauteville) is thought to have initiated the rebuilding of the cathedral (founded AD 845) in 1080, the date of a letter from Pope Gregory VII (1073-1085) to Archbishop Alfanus (died 1085). The cathedral was consecrated by the Pope in 1084, when it was only partially complete. To the west of the cathedral, the Porta dei Leoni leads to a spacious atrium (36 x 33 m) surrounded by a two-storey arcade; the gallery reflects Islamic influences, with its decoration of polychrome inlay and black and yellow tufa for the extrados of the arches. The designs that decorate the architraves and doorposts include inhabited rinceaux and palm-trees; pairs of small lions in high relief are at the base of each door. The campanile is dated by inscription to 1137-1152. The crypt is believed to house the remains of St. Matthew.