In architecture, a semicircular arch or round arch is a type of arch "Arch (construction)") that in the intrados has the shape of a semicircle.

The semicircular arch was already used in Mesopotamia (Chaldean architecture) in the third millennium BC. C. Its use passed to Etruscan architecture, and from this to the Romans. It is characteristic of Roman art and the styles that derived from it, such as Romanesque architecture, Renaissance architecture and Baroque architecture.

It was also used in bridges, as is the case of the Villanueva-Ramplay bridge, which has several semicircular arches.

Starting from the basic form of an arch with a single center, some variants of the semicircular arch can be distinguished:

From the point of view of material resistance, the geometry and characteristics of a semicircular arch mean that all its points work in compression. Each voussoir has a state similar to that of a wedge "Wedge (machine)") compressed on its lateral faces.