§ 32. While, in the districts to which allusion has just been made, towers were designed, as a rule, with a view to the spires which were to cover them, the tower, in other parts of England, was designed simply as a tower, and the spire was regarded merely as a roof for it. In the chalk country north of the Thames, towers are often found crowned by small timber spirelets with a leaden covering, which are merely insignificant additions. Towards the middle of the fourteenth century, an important development in the elevation of the main fabric led to a general disuse of the spire, especially in districts where stone spires had formed no part of architectural design. Clerestories with broad windows were built above the arcades of the nave. With this increase of height the old high pitched roofs were abandoned in favour of roofs of a flatter pitch. Very often, this was due to the rotting of the old roof-timber at the ends next the wall-plates. These ends were sawn off, and the roof re-laid at a lower pitch. At the same time, the clerestory dwarfed the western tower. At Oadby, near Leicester, where there is a beautiful tower and spire, designed in perfect harmony with a fourteenth century nave, the fifteenth century clerestory actually raises the height of the nave to that of the tower, with incongruous effect. During the fifteenth century, therefore, it is common to find that towers were rebuilt, or an upper story was added to them, in proportion to the increase of height in the nave. Thus, at Immingham in north Lincolnshire, the clerestory and upper part of the tower are of one date, and were built as part of one connected work. The roof of the clerestory being, in most cases, nearly flat, the roof of the tower followed suit; and although, where traditions of spire design had a hardy existence, spires were still built, towers without spires, surmounted by parapets like the parapets which hid the roof of the clerestories, became the order of the day. In certain parts of England, and especially in Somerset, where the art of designing towers was pursued with extraordinary success, towers were rebuilt from the ground. But the proportion of towers, with or without spires, which have been heightened to meet the requirements of a clerestory, is probably in excess of the proportion of towers entirely rebuilt. In the case of heightened towers, the pitch of the older roof of the nave can generally be made out by the retention of its housing slot or weather course in the east wall of the tower. At Gedney, in south Lincolnshire, where the lower part of the tower is of the thirteenth century, the line of the contemporary roof may be traced above the tower arch. Above this is another line, marking the pitch of a new roof, made when the arcades were rebuilt in the fourteenth century. The clerestory and the upper story of the tower belong to the fifteenth century. In many instances, however, the flattening of the roof has followed the rebuilding of the tower; and in these the old weather course will be found on the east face of the tower, above the present roof, as in the south aisle at St Mary's, Leicester. Here the roof was probably flattened in the fifteenth century, when the tower and spire were completed.