Afour-centred arch (Commonwealth spelling) orfour-centered arch (American spelling) is a low, wide type ofarch with a pointedapex. 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 flatteneddepressed 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 thePersian arch, which is moderately "depressed" and found inIslamic architecture, and theTudor arch, which is much flatter and found inEnglish architecture. Another variant, thekeel arch, has partially straight rather than curved sides and developed inFatimid architecture.^[a]

The four-centered arch is widely used in Islamic architecture, originally employed by theAbbasids and later by theFatimids and byPersianate cultures. The earliest examples of a four-centered arch were introduced atSamarra, a purpose-built capital built by theAbbasids in the 9th century. Here they are found in the portals of the Qubbat al-Sulaiybiyya, an octagonal pavilion, and theQasr al-'Ashiq palace.^{[3][4]: 25, 250–251} Later, the four-centered arch appeared commonly in the architecture of theGhurid Empire, which ruled over large parts of Iran, Central Asia, and the northern Indian Subcontinent in the 12th to 13th centuries.^[3] It was very common in the architecture of theTimurid Empire and its successor states, becoming a standard form of widerIranian architecture and laterMughal architecture.^{[3][4]: 200, 283} In this Persianate cultural sphere it was used for forms such asarcades, windows, gateways, andiwans.^[3] Pointed three-centered arches were also frequently used in Iran and Central Asia.^{[5][4]: 283}

A variant of the four-centered arch, typically referred to as the "keel arch", became especially characteristic of Fatimid architecture.^[3][6][7] It is distinguished from other four-centered arches by having most of the arch's normal radius appear more straight than curved.^[3] It became standard for a while in Egyptian Islamic architecture in the 12th century.^[3]Blind keel arch niches appeared frequently as a motif of decorated façades in late Fatimid,Ayyubid, and earlyMamluk architecture in Cairo.^{[3][8][4]: 46, 285}

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  Restored 9th century arches of the Qasr al-'Ashiq,Samarra.
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  The 11th/12th centuryBaghdad Gate,Raqqa.
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  Keel arches in the façade of theal-Salih Tala'i Mosque inCairo (1160, lateFatimid period)
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  The 13th centurycorbelled arches of theQuwwat ul-Islam Mosque,Delhi.^[9]
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  The 16th century western gate of thePurana Qil'a fortress,Delhi.
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  The 16th centuryJama Mosque inBijapur with rib vaulting consisting of four-centred arches.
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  The 16th centuryJahangiri Mahal at theAgra Fort has a four-centred arched gateway flanked by four-centred blind arches.
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  The 17th centuryTaj Mahal mausoleum ofMumtaz Mahal inAgra.
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  The 17th century south-eastern gateway of theLalbagh Fort in Dhakkar.
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  The 17th centuryBara Kaman mausoleum ofAli Adil Shah II in Bijapur.

In English architecture the arch is often known as a Tudor arch, as it was a common architectural element during the reigns of theTudor dynasty (1485–1603), though its use predates 1485 by several decades, and from about 1550 it was out of fashion for grand buildings. It is a blunted version of thepointed arch ofGothic architecture, of whichTudor architecture is the last phase in England.^[10] However, a Tudor arch, while similar in appearance, is not truly four-centred, as it has two straight sides instead of large shallow curves.

The four-centred arch was especially used for doorways, where it gives a wide opening without taking too much space above, compared to a more pointedtwo-centred arch. This first appeared on a major scale in the west porch ofWinchester Cathedral, of uncertain date but likely mid-fourteenth century.^[11] InTudor architecture of the grander sort it is so used when the window openings are rectangular, as for example atHampton Court Palace.

A notable early example is the west window ofGloucester Cathedral. There are three royal chapels and one chapel-like Abbey which show the style at its most elaborate:King's College Chapel,Cambridge;St George's Chapel, Windsor;Henry VII's Chapel atWestminster Abbey, andBath Abbey. However, numerous simpler buildings, especially churches built during the wool boom inEast Anglia and the Cotswolds, also demonstrate the style.

When employed to frame a large church window, it lends itself to very wide spaces, decoratively filled with many narrow verticalmullions and horizontaltransoms. The overall effect produces a grid-like appearance of regular, delicate, rectangular forms with an emphasis on the perpendicular, characteristic of the style, known asPerpendicular Gothic in England, of the 15th and early 16th centuries. This is very similar to contemporarySpanish style in particular. In buildings such as Hampton Court the Tudor arch is found together with the first appearance ofRenaissance architecture in England, much later than inItaly. In the later period it is generally only used for major decorative windows, perhaps in anoriel window, or a bay window supported on abracket orcorbel.^[12][13]

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  Gloucester Cathedral, west window, c. 1420
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  King's College Chapel, Cambridge, begun 1446
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  Great Gate,Trinity College, Cambridge (inside), 1519–35
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  Clock Court gatehouse,Hampton Court Palace, c. 1520
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  St. George's Chapel, Windsor, east window, 1475–1528
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  Small doorway, now blocked, in a church

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