The tower is 22 feet 6 inches square, with walls about 5 feet in thickness. It is awkwardly placed in connection with the church, the walls not being parallel to those of the nave, while the tower projects into the south aisle from 6 feet to 7 feet 6 inches. A high window in the east wall of the ground floor of the tower is, in consequence, built up by the wall of the aisle. The ground floor has a pointed ribbed barrel vault, and a wheel stair in the south-west angle leads to the top. The doorway of the tower is in the north wall, and now enters from the south aisle of the nave (Fig. 510); but, so far as can be ascertained, the doorway appears to have been originally an external one. The sill is about 3 feet above the existing level of the floor of the nave. It has a nook shaft on each side, with the usual Norman cap and base, and a semicircular arch head. There is no appearance of any building having originally been joined to, or abutted against, the tower, which would therefore seem to have stood detached. It would thus be to a certain extent in accordance with the traditional design, being detached like the Irish towers, though square on plan, not round like them. It also resembled the Irish towers in having the doorway raised some feet above the ground. As Dunblane was several times pillaged and destroyed by the Norsemen, the tower may have been intended, as the ancient round towers were, to serve as a place of defence against such inroads, as well as for a belfry. The tower (Fig. 511) is six stories in height. The lower four of these stories form part of the original structure, and have small narrow apertures, except the fourth story, which was probably the original top story or belfry, and has a two-light window on each side. These consist of an opening with plain jambs and round arched head, divided into two lights by a central shaft having Norman cap and base and two small plain round arched heads within the outer arch. The four lower stories of the tower are all built with red freestone, the fifth story is of yellow freestone, the sixth or top story of a grey freestone, and the tower is finished with a parapet of red freestone. The two highest stories are evidently of a late date. The top story contains a large pointed window on each side with a central mullion. The form of these windows is inelegant, and they are probably of sixteenth century date. The parapet, with its angle bartisans resembling those of the castles of the sixteenth and seventeenth centuries, but with almost no projection, is apparently still later than the belfry story. On the parapet are the arms of Bishop Chisholm, about 1500. The slated [Illustration: FIG. 510.--Dunblane Cathedral. South Side of Nave and Lower Story of Tower.] [Illustration: FIG. 511.--Dunblane Cathedral. Tower from South-East and Part of Choir.] wooden roof is comparatively modern, but is on the lines of the one which preceded it.