It is not, however, what Elias de Dereham, the original architect, meant. No spire, or even upper tower, says Sir Christopher Wren, was originally contemplated. The unique slenderness of the piers of the crossing is certain evidence of that. The diameter of the piers on which the central tower of Canterbury rests is twelve feet; those at York and Winchester have a diameter of ten feet; those at Worcester nine feet; those of Peterborough tower (which collapsed) and of Salisbury, seven feet only. It is almost terrible to stand between these four thin piers of Salisbury and think how many hundred tons of stone in tower and spire above they have been made to bear. They were never meant to bear any such weight, especially planted as they are, like the whole cathedral, on the insecure foundation of a spongy bog. Indeed, not merely the tower and spire, but the whole cathedral, ought never to have been built where they are. Recklessness is by no means a strong enough word to use of the mediæval builders’ wanton carelessness about foundations. Peterborough cathedral was built practically without foundations on waterlogged peat; beneath the central tower of Carlisle cathedral were two running springs; Wells is reared on the boggy shores of a ring of pools. At Salisbury continuous bases had to be built from pier to pier. [Illustration: RETRO-CHOIR, LOOKING WEST.] Elias de Dereham’s design, no doubt, was to give us an exterior something like that of Beverley Minster or Westminster Abbey. The whole elevation of the cathedral, however, clamoured for a tall tower and spire. The original design was abandoned, and the foolhardy enterprise was taken in hand (_c._ 1330) of adding to the existing tower, which only just rose above the roofs, two more stages, and on these a spire, and that not of wood, but of stone. To abut this perilous steeple as much as possible, great flying-buttresses were added, both externally and running through the clerestory and triforium of the interior of the church. Moreover, to lessen the weight, the tower-walls were built in thin shells, while the spire is but nine inches thick. That the builders left their timber scaffolding in the spire, where it still is, to give its sides a little additional support, shows that they were alive themselves to the fragility and insecurity of their work. Later on, in the fifteenth century, stone girders were put across the piers of the central and eastern transepts, as at Canterbury and Wells, by way of struts, to keep the piers from bulging inwardly, though, as a matter of fact, what was wanted was rather ties to keep them from bulging outwardly.