Arch

Curved structure that spans a space and may support a load

An arch is a curved vertical structure spanning an open space underneath it. Arches may support the load above them, or they may perform a purely decorative role. As a decorative element, the arch dates back to the 4th millennium BC, but structural load-bearing arches became popular only after their adoption by the Ancient Romans in the 4th century BC. Arch-like structures can be horizontal, like an arch dam that withstands a horizontal hydrostatic pressure load.

From Wikipedia, under CC BY-SA. More on occurri.