A four-centred arch or four-centered arch is a low, wide type of arch with a pointed apex. Its structure is achieved by drafting two arcs which rise steeply from each springing point on a small radius, and then turning into two arches with a wide radius and much lower springing point. It is a pointed sub-type of the general flattened depressed arch. This type of arch uses space efficiently and decoratively when used for doorways. It is also employed as a wall decoration in which arcade and window openings form part of the whole decorative surface. Two of the most notable types are known as the Persian arch, which is moderately "depressed" and found in Islamic architecture, and the Tudor arch, which is much flatter and found in English architecture. Another variant, the keel arch, has partially straight rather than curved sides and developed in Fatimid architecture.
Tudor arch at Layer Marney Tower, 1520s
Persian arches on the Si-o-se-pol bridge, Isfahan, c. 1600
The 17th century Buland Darwaza at Fatehpur Sikri has a four-centred archway with vaulted iwan.
Restored 9th century arches of the Qasr al-'Ashiq, Samarra.
An arch is a curved vertical structure spanning an open space underneath it. Arch can either support the load above it or perform a purely decorative role. The arch dates back to fourth millennium BC, but became popular only after its adoption by the Romans in the 4th century BC.
Gateway Arch
A complex funicular model (Church of Colònia Güell by Gaudi, 19th century)
Arcades of Pont du Gard (Roman)
Separating arches in the St. Zeno church [de]