"There is a remarkable property of shells supported vertically at their edges. [Take] a spherical dome supported on a wall. A tension tie is required around the perimeter at the intersection of the dome and the wall. This tie will be funicular, i.e., it will only carry axial tension forces. This principle has been known since antiquity for circular domes and ties. However... the tie will be funicular for any shape of either the plan or elevation (Csonka 1962) provided that the shell has positive curvature and continuous vertical support. The support may be a continuous wall or stiff beams between adequately spaced columns. ...The thrusts are taken by shear forces through the width of the shell, and only tension forces exist in the tie."