Four-centred arch

Use in Islamic architectureThe four-centered arch is widely used in Islamic architecture, originally employed by the Abbasids and later by the Fatimids and by Persianate cultures. The earliest examples of a four-centered arch were introduced at Samarra, a purpose-built capital built by the Abbasids in the 9th century. Here they are found in the portals of the Qubbat al-Sulaiybiyya, an octagonal pavilion, and the Qasr al-'Ashiq palace. Later, the four-centered arch appeared commonly in the architecture of the Ghurid Empire, which ruled over large parts of Iran, Central Asia, and the northern Indian Subcontinent in the 12th to 13th centuries. It was very common in the architecture of the Timurid Empire and its successor states, becoming a standard form of wider Iranian architecture and later Mughal architecture. In this Persianate cultural sphere it was used for forms such as arcades, windows, gateways, and iwans. Pointed three-centered arches were also frequently used in Iran and Central Asia. A variant of the four-centered arch, typically referred to as the "keel arch", became especially characteristic of Fatimid architecture. It is distinguished from other four-centered arches by