The arch, is a type of bow that has the shape of a semi-circle in the intrados. Therefore, the center of the arch is located at the level of the lines of the Imposts.
It began to be used in Mesopotamia in the third millennium BC. Use passed into Etruscan architecture, and this to the Romans, who spread it by regions of the Mediterranean. It is characteristic of Roman art and all styles that derived from it, such as Romanesque architecture, Renaissance architecture and Baroque architecture.
The geometry and features of a semicircular arch makes all their points work in compression. If we look at the façade, we see that each segment has a status similar to a wedge compressed in its lateral faces.