What physical and technological structures show the importance of circles?

Question

What physical and technological structures show the importance of circles?

Answer 1

Anything that need to distribute a load to reduce stress (increase strength).

Domes (Rotunda's)

Arches (Bridges, aquaducts)

Round Cylindrical tanks

Spherical pressure tanks

Answer 2

A structure where the circle plays a very important rule is the submarine. The hull of the submarine must be as circular in cross section as possible in order that the stress on the hull which is subjected to external pressure loading can be predicted.This is exactly why circularity measurements are done during the construction of the submarine hull and also during repairs on the hull. Any serious deviation from an acceptable range in circularity is not allowed because it might lead to collapse of the hull under high external pressure loading.