Of the spires, one rises from the central tower and one surmounts each of the towers which flank the west front. The central spire dates only from the Restoration, the older spire having been entirely destroyed in the Civil Wars. There is no doubt that the original spire was different in appearance to the present one, which is an imitation of the western spires, carried out in the spirit of the Perpendicular style. What the earlier spire was really like is doubtful, neither is it quite certain when it was built, though the central tower was probably rebuilt about 1250, when it is supposed that the intention was to retain the Norman nave. What the height and pitch of the roof of the old Norman nave must have been can be seen from the old housing course which remains to this day above the nave groining. "It was the custom," as Mr J. O. Scott explained in a lecture on the cathedral, "of old builders, as of modern builders, to insert in any wall against which a roof abuts a projecting course of stone, called a 'housing,' following the slope of the roof, the object being to keep the wet from getting in between the roof and the wall. And so when the central tower was rebuilt, there was the Norman nave to which the new work had to be fitted. Hence, at this time the builders inserted a 'housing course' of masonry into the west wall of the new tower, to protect the junction of the old Norman nave roof from the weather." These disused housing courses can constantly be seen in old churches, sometimes several, one above the other, showing the changes in the roofing of the church. The present spire is said vaguely to have been erected from the designs or under the direction of Sir Christopher Wren; but the tradition which connects this great modern architect with the cathedral is very uncertain. [Illustration: THE CATHEDRAL FROM THE MINSTER POOL.] The two western spires were probably built in Bishop Norburgh's time, and possibly were finished in the time of his successor; but the north-west spire has been rebuilt from the belfry windows upwards in imitation of the old work, but, like the central tower, in the Perpendicular manner. The south-west or Jesus Tower, which is a little higher than the other, has also had its two upper storeys rebuilt. The spires are octagonal, and are divided into six compartments. In the western spires the four lower compartments have windows of two lights each with acute crocketted pediments. There are only four windows in the lowest compartment; but in the second, third, and fourth compartments there is a window in each face; the fifth is panelled between crocketted ribs, and the top compartment is plain with small windows. All the spires are open all the way up without any inside supports.