Good example of Chesterton's Fence: Lateral iron supports between the flying buttresses: it is not known when these external tie rods were installed. The technology would have been available at the time of the initial construction, but the extra support might not have been considered necessary until after the collapse in 1284, or even later. In the 1960s, the tie rods were removed; the thinking was that they were ungraceful and unnecessary. However, the oscillations created by the wind became amplified, and the choir partially disassociated itself from the transept. Subsequently, the tie rods were reinstalled, but this time with rods made of steel. Since steel is less ductile than iron, the structure became more rigid, possibly causing additional fissures.