A corbelarch is an arch-like construction method that uses the architectural technique of corbeling to span a space or void in a structure, such as an entranceway in a wall or as the span of a bridge. A corbel vault uses this technique to support the superstructure of a building's roof. A corbel arch is constructed by offsetting successive courses of stone at the springline of the walls so that they project towards the archway's center from each supporting side, until the courses meet at the apex of the archway. For a corbeled vault covering, the technique is extended in three dimensions along the lengths of two opposing walls. , Bronze Age Syria. Although an improvement in load-bearing efficiency over the post and lintel design, corbeled arches are not entirely self-supporting structures, and the corbeled arch is sometimes termed a false arch for this reason. Unlike "true" arches, not all of the structure's tensile stresses caused by the weight of the superstructure are transformed into compressive stresses. Corbel arches and vaults require significantly thickened walls and an abutment of other stone or fill to counteract the effects of gravity, which otherwise would tend to collapse each side of the archway inwards. Some arches use a stepped style, keeping the block faces rectangular, while other form or select them to give the arch smooth edges, usually with a pointed shape.
Use in historical cultures
Ireland
The Newgrange passage tomb has an intact corbel arch supporting the roof of the main chamber, and the buildings of the monastery at Skellig Michael are constructed using this method.
Ancient Egypt
During the Fourth Dynasty reign of PharaohSneferu, the Ancient Egyptian pyramids used corbel vaults in some of their chambers. These monuments include the Meidum Pyramid, the Bent Pyramid and its satellite pyramid, and the Red Pyramid. The Great Pyramid of Giza uses corbel arches at the Grand Gallery. The Egyptians discovered the principle of the true arch early on, but continued to use the corbel arch in many buildings, sometimes mixing the two in the same building. In particular they avoided the true arch in temples as long as these were constructed, preferring rectangular openings with a straight lintel.
Ancient Mediterranean
Corbel arches and vaults are found in various places around the ancient Mediterranean. In particular, corbelled burial vaults constructed below the floor are found in Ebla in Syria, and in Tel Hazor, and Tel Megiddo in Israel. Ugarit also has corbelled constructions. Nuraghe constructions in ancient Sardinia, dating back to 1900 BC, use similar corbel techniques. The use of beehive tombs on the Iberian peninsula and elsewhere around the Mediterranean, going back to 3000 BC, is also similar.
The Hittites in ancient Anatolia were also building corbelled vaults. The earliest ones date to the 16th century BC. Some similarities are found between the Hittite and Mycenaean construction techniques. Yet the Hittite corbelled vaults are earlier by about 300 years.
Corbeled arches are a distinctive feature of certain pre-Columbian Mesoamerican constructions and historical/regional architectural styles, particularly in that of the Maya civilization. The prevalence of this spanning technique for entrances and vaults in Maya architecture is attested at a great many Maya archaeological sites, and is known from structures dating back to the Formative or Preclassic era. By the beginning of the Classic era corbeled vaults are a near-universal feature of building construction in the central Petén Basin region of the central Maya lowlands.
India
Before the true arch was introduced in Indo-Islamic architecture, almost all the arches in Indian buildings were trabeated or corbelled. In North India in the state of Orissa, "the later temples at Bhubaneswar were built on the principle of corbelled vaulting, which is seen first in the porch of the Mukteswar and, technically speaking, no fundamental change occurred from this time onwards." The earliest large buildings of the Delhi Sultanate established in 1206 after a Muslim invasion used Indian workers used to Hindu temple architecture, but the patrons were used to Central Asian styles that used true arches heavily. Corbel arches, the largest of exceptional size, were used in the massive screens in front of the Quwwat-ul-Islam Mosque in Delhi, begun in 1193, and the Adhai Din Ka Jhonpra mosque, Ajmer, Rajasthan, c. 1229. These are examples of Islamic architecture drawing on Persia and Central Asia, where builders were well used to the true arch, that stick with the corbelled arch that Indian builders were used to. It took almost a century from the start of the Delhi Sultanate in 1206 for the true arch to appear. By around 1300 true domes and arches with voussoirs were being built; the ruined Tomb of Balban in the Qutb complex in Delhi may be the earliest survival.
The candi or temples of Indonesia which were constructed between 8th to 15th century, made use of corbel arch technique to create a span opening for gate or inner chamber of the temple. The notable example of corbel arch in Indonesian classic temple architecture are the arches of Borobudur. The interlocking andesite stone blocks creating the corbel arch, are notable for their "T" formed lock on the center top of the corbel arch.
Cambodia
All the temples in Angkor made use of the corbel arch, between the AD 9th and 12th centuries.
