In architecture, a triangular arch typically defines an arch where the intrados (inner surface of an arch) consists of two straight segments formed by two stone slabs leaning against each other.[1][2] In this roof-like[3] arrangement, mitre joint is usually used at the crown, thus the arch was in the past also called a mitre arch.[4] Brick builders would call triangular any arch with straight inclined sides.[5] Mayan corbel arches are also sometimes called triangular due to their shape.[6]
Since the sides of a triangular arch are experiencing bending stress, it is a false arch[2] in a structural sense (historically preceding the invention of true arches[7] and going back to Neolithic times[8]). The design was common in Anglo-Saxon England until the late 11th century (St Mary Goslany).[1]