The inherent weight (dead weight) of any bridge can cause it to collapse, so reducing weight is often a key consideration in design.Creating holes in the space between the extrados, the exterior curve of an arch, and the abutment not only reduces the weight of the bridge, but also allows flood water to pass through, reducing the bridge’s resistance to water. These practical voids are called open spandrels, as seen above in the Pontypridd Bridge in southern Wales.