Editing Arch (section)

=== Masonry ===
The [[voussoir]]s can be wedge-shaped or have a form of a [[rectangular cuboid]], in the latter case the wedge-like shape is provided by the [[Mortar (masonry)|mortar]].<ref name=treccani1991>{{Treccani|arco_(Enciclopedia-dell'-Arte-Medievale)|arco|C. Ewert|1991}}</ref> 

An arch is held in place by the weight of all of its members, making construction problematic. One answer is to build a frame (historically, of wood) which exactly follows the form of the underside of the arch. This is known as a centre or [[centring]]. [[Voussoir]]s are laid on it until the arch is complete and self-supporting. For an arch higher than head height, [[scaffolding]] would be required, so it could be combined with the arch support. Arches may fall when the frame is removed if design or construction has been faulty.{{Citation needed|date=February 2011}} 

Old arches sometimes need reinforcement due to decay of the [[Keystone (architecture)|keystones]], forming what is known as [[bald arch]].