A higher resolution image, from a slightly different viewpoint
The roof of the Throne Room of the Taq-i-Kisra in Iran is the best surviving example of an ancient large span structure built to a catenary profile, the shape that will minimise bending moments in a structure of uniform thickness, standing under its own weight.
The red line added to the photograph is a catenary, and the blue line a parabola with the same span at first floor level. The plot suggests that the roof shape from first floor level does indeed approximate a catenary, although the low resolution photograph and irregular outline of the end face of the structure make it difficult to be certain.
Filed under: Newton | Tagged: Arch structure, Catenary
Looks like a cantenary on the inside and a parabola on the outter surface. Looks a bit like a bit of thickening in the structure at the base of the arch
[...] hence the ideal shape for an arch. The same realisation was apparently used by the builders of the The Roof of the Taq-i-Kisra some 1000 years earlier, but in general the shape of large span arch structures is not a catenary, [...]