Keyser, RUDOLPH

1803-1864. Norwegian historian. Keystone. Commonly, uppermost and central vou oir of an arch, although the mechanical function of this does not differ from that of any other stone of the arch, each being nece ary to lock the arch. The fact that the upper stone is put in last Keystone in the church Pont de l'Arche, Normandy, 1516. has probably given rise to the name. In Roman and Renai ance architecture the so-called keystone is often distinguished in treatment, being projected and embellished with a mask or other carved ornament.