[L. arcus. Fr. arche.] A self-sustaining structure, usually of a curved form, made up of separate wedge-shaped solids, with the joints between them disposed in the direction of the radii of the curve, used to support the wall or other weight above an opening. The beginning of the arch is called the spring, the two bottom stones being the springers, the middle the crown or keystone, and the parts between the crown and the spring the haunches. A flat arch is constructed of stones cut into wedges or other shapes, so as to support each other without rising into a curve.