Semicircular arch



In architecture, a semicircular arch is an arch with an intrados (inner surface) shaped like a semicircle. This type of arch was adopted and very widely used by the Romans, thus becoming permanently associated with Roman architecture.

Terminology
When the arch construction involves the Roman techniques (either wedge-like stone voussoirs or thin Roman bricks), it is known as a Roman arch. The semicircular arch is also known as a round arch.

Description
The rise (height) of a round arch is limited to $1/2$ of its span, so it looks more "grounded" than a parabolic arch or a pointed arch. Whenever a higher semicircular arch was required (for example, for a narrow arch to match the height of a nearby broad one), either stilting or horseshoe shape were used, thus creating a stilted arch (also surmounted ) and horseshoe arch respectively. These "shifts and dodges" were immediately dropped once the pointed arch with its malleable proportions was adopted. Still, "the Romanesque arch is beautiful as an abstract line. Its type is always before us in that of the apparent vault of heaven, and horizon of the earth" (John Ruskin, "The Seven Lamps of Architecture").

A round arch that sits atop the corbels, with corbels rounded to create a bell-like shape of intrados, is called a bell arch.

When the architecture of the building dictates the rise of he arch to be less that $1/2$ of its span (for example, in Roman residential construction), a segmental arch with a rounded shape that is less than a semicircle can be used.

History and associated styles
The popularity of the semicircular arch is based on simplicity of its layout and construction, not superior structural properties. The sides of this arch swing wider than the perfect funicular curve and therefore experience a bending moment with the force directed outwards. To prevent buckling, heavy surcharge (fill), so called spandrel, needs to be applied outside of the haunches.

In addition to the Imperial Roman construction, round arches are also associated with Byzantine, Romanesque (and Neo-Romanesque), Renaissance and Rundbogenstil styles. While the semicircular arch was known in the Greek architecture, it mostly played there a decorative, not structural, role.