DISCHARGING ARCH, in architecture, an arch (q.v.) built over a lintel or square-headed opening, so as to take the weight of the wall above off the horizontal head of the opening. In the great pyramid of Giza (c. 300o B.c.), the entrance passage is roofed with slabs of stone, but above these, great blocks, set leaning against each other at the top so as to leave a triangular space beneath, form what is probably the earliest discharging arch extant. Discharging arches of circular or segmental shape are frequent in Roman buildings, and by the time of Diocletian, the custom of decorating these arches with an architrave had arisen. This usage, which apparently was of Syrian origin, became rather common during a considerable part of the Byzantine period of architecture.