Thehorseshoe arch (Arabic:قوس حدوة الحصان;Spanish:arco de herradura), also called theMoorish arch and thekeyhole arch, is a type of arch in which the circular curve is continued below the horizontal line of its diameter, so that the opening at the bottom of the arch is narrower than the arch's full span.^[1][2][3] Evidence for the earliest uses of this form are found inLate Antique andSasanian architecture, and it was then used in Spain by theVisigoths. But in the 19th century, perhaps when these earlier uses had not been realized, it became emblematic ofIslamic architecture, especiallyMoorish architecture andMozarabic art inIberia. It also made later appearances inMoorish Revival andArt Nouveau styles. Horseshoe arches can take rounded, pointed orlobed form.

The origins of the horseshoe arch are complicated.^[5] It appeared in pre-IslamicSasanian architecture such as theTaq-i Kasra in present-dayIraq and thePalace of Ardashir in southwesternIran (3rd century CE).^[6][5][4] It also appeared in Late Roman orByzantine architecture, as well as inRoman Spain.^[7] In ByzantineSyria,^[5] the form was used in theBaptistery of Saint Jacob atNusaybin (4th century CE)^[8] and inQasr Ibn Wardan (564 CE).^[9]

Another possible origin of the horseshoe arch motif is India, whererock-cut temples with mildly incurved horseshoe arches survive from early periods, though these were sculpted in rock rather than constructed, and probably imitate earlier forms in wood.^[10][4] For example, horseshoe arch shapes are found in parts of theAjanta Caves andKarla Caves dating from around the 1st century BCE to 1st century CE.^[11]

Horseshoe arches made of baked brick have been found in the so-called Tomb of the Brick Arches inAksum (present-dayEthiopia), built during theKingdom of Aksum and tentatively dated to the 4th century CE.^[10][12] In a 1991 publication, archeologist Stuart C. Munro-Hay suggests that these could be evidence that transmission of architectural ideas took place via routes not previously considered by scholars. He suggests that the brick-built horseshoe arches could have been an Aksumite innovation based on ideas transmitted via trade with India.^[10]

Further evidence of their use is also found inearly Christian architecture in ByzantineAnatolia and became characteristic of Christian architecture inCappadocia,^[13][14][15] though the origins of this regional feature are sometimes debated.^[a] An early example of its use in Anatolia is found at theAlahan Monastery in present-day southernTurkey,^[13] dating most likely from the 5th century CE.^[19] InVisigothic Spain, horseshoe arches are found, for example, in of theChurch of Santa Eulalia de Boveda nearLugo and theChurch of Santa Maria de Melque nearToledo.^[20] Some tombstones from that period have been found in the north of Spain with horseshoe arches in them, eliciting speculation about a pre-Roman localCeltic tradition.^[21]

In earlyIslamic architecture, some horseshoe arches appeared inUmayyad architecture of the 7th to 8th centuries. They are found in theUmayyad Mosque ofDamascus, though their horseshoe shape is not very pronounced.^[23][24] They are also found in theUmayyad Palace at theAmman Citadel in present-dayJordan.^[5]

According to Giovanni Teresio Rivoira, an archeologist writing in the early 20th century, the pointed variant of the horseshoe arch is of Islamic origin.^[25] According to Rivoira, this type of arch was first used in theIbn Tulun Mosque,^[25] completed in 879.^[26]Wijdan Ali also describes this as the first systematic use of the pointed variant.^[27] Horseshoe arches of a slightly pointed form were also used inAghlabid architecture of the 9th century,^[28]: 45 including theGreat Mosque of Kairouan (circa 836) and theMosque of Ibn Khayrun (866).^[29][30]

It was inAl-Andalus (on theIberian Peninsula) and westernNorth Africa (theMaghreb) that horseshoe arches developed their characteristic form. Prior to theMuslim invasion of Spain, theVisigoths of the Iberian Peninsula used them intheir architecture.^[31][7][32] Although it is possible that Andalusi architecture borrowed the horseshoe arch from Umayyad Syria, these local precedents make it just as likely that it developed locally instead.^[33]: 43 The "Moorish" arch, however, was of a slightly different and more sophisticated form than the Visigothic arch, being less flat and more circular.^{[28]: 163–164 [33]: 43}

TheUmayyads of Al-Andalus, starting with theEmirate period, used horseshoe arches prominently and ubiquitously, often enclosing them in analfiz (rectangular frame) to accentuate the effect of its shape.^[28]: 45 This can be seen at a large scale in their major work, theGreat Mosque of Córdoba.^[29] Its most distinctive form, however, was consolidated in the 10th century during theCaliphal period, as seen atMadinat al-Zahra, where the arches consist of about three quarters of a circle and are framed in analfiz.^[34] The Córdoban style of horseshoe arch spread all over the Caliphate and adjacent areas, and was adopted by the successor Muslim emirates of the peninsula, thetaifas, as well as by the architecture of the Maghreb under subsequent dynasties. Its use remained especially consistent in the form of mosquemihrabs.^[28]: 232

In the northern Iberian Peninsula, whereAsturias and other Christian kingdoms ruled, the use of horseshoe arches continued under the influence of previous Visigothic architecture and of contemporary Islamic architecture.^[35] The addition of analfiz around horseshoe arches was one detail more specifically borrowed from Islamic styles.^[35] Starting in the 9th century, someMozarabs (Christians living under Muslim rule) left al-Andalus and settled in the northern Christian territories,^[b] where they contributed to popularizing this form locally, as exemplified bySan Miguel de Escalada (10th century).^[36][37][38] The Mozarabs also incorporated horseshoe arches into their art, such as inilluminated manuscripts.^[39][40]

Under theAlmoravids (11th-12th centuries), the first pointed horseshoe arches began to appear in the region and then became more widespread during theAlmohad period (12th-13th centuries). This pointed horseshoe arch is likely of North African origin.^[28]: 234 Art historianGeorges Marçais attributed it in particular toIfriqiya (present-dayTunisia), where it was present in earlier Aghlabid andFatimid architecture.^[28]: 234

As Muslim rule retreated in Al-Andalus, theMudéjar style, which developed from the 12th to the 16th centuries under Spanish Christian rule, continued the tradition of horseshoe arches in the Iberian Peninsula.^[41] Horseshoe arches also continued to be used in the Maghreb, in thearchitecture of Morocco,Algeria, andTunisia.^[42][28]

• 
  Church of Santa Eulalia de Bóveda near Lugo, Spain (4th-5th century),^[43] early Christian or Visigothic period
• 
  Church of San Juan de Baños in Spain (mid-7th century)^[44]
• 
  Prayer hall of theGreat Mosque of Córdoba, Spain (late 8th century)
• 
  Horseshoe arches in theGreat Mosque of Kairouan, Tunisia (9th century)
• 
  Church ofSan Miguel de Escalada nearLeón, Spain (10th century); an example ofMozarabic orRepoblación architecture
• 
  Arches withalfiz in the Mozarabic Church ofSantiago de Peñalba (10th century)^[45]
• 
  Mihrab of the Great Mosque of Córdoba (10th century), with horseshoe arch opening surrounded by a rectangularalfiz
• 
  Caliphal-style arches of theTaifa palace (11th century) in theAlcazaba of Málaga, Spain
• 
  Pointed horseshoe arches in theMosque of Tinmal, Morocco (12th century), typical of theAlmohad period and afterwards
• 
  Mudéjar architecture in theChurch of San Roman inToledo, Spain (12th or 13th century)^[46]
• 
  Bou Inania Madrasa ofFez, Morocco (14th century), from theMarinid period
• 
  Pointed horseshoe arches inDar Mustapha Pasha inAlgiers, Algeria (1799)^[47]

Horseshoe arches were also common inGhurid andGhaznavid architecture (11th-13th centuries) inCentral Asia, though in this region they had sharp pointed apexes, in contrast with those of the western Islamic world. Sometimes they were cusped or given multifoil flourishes.^[48] Around the same time or not long afterward, they begin to appear as far east asIndia,^[48] inIndo-Islamic architecture, such as in theAlai Darwaza gatehouse (dating from 1311) at theQutb Complex inDelhi,^[49] though they were not a consistent feature in India.

Some pointed arches with a slightly horseshoe shape appear inAyyubid architecture in Syria.^[50] It appears, exceptionally, in some instances ofMamluk architecture. For example, it appears in some details of theSultan Qalawun Complex in Cairo, built in 1285.^[51] Andalusi-style horseshoe arches are also found alongside the minaret of the Mosque of Ibn Tulun in Cairo, probably dating from 13th-century renovations ordered bySultan Lajin to the older 9th-century mosque.^[52]

In addition to their use across the Islamic world, horseshoe arches became popular in Western countries inMoorish Revival architecture, which became fashionable in the 19th century. They were widely used in Moorish Revival synagogues.^[54][55] They were employed in theNeo-Mudéjar style in Spain, another type of Moorish Revival style.^[56] They are used in some forms ofIndo-Saracenic Revival architecture, a 19th-century style associated with theBritish Raj.^[56]

Exaggerated horseshoe arches were also popular in some forms ofArt Nouveau architecture, notably inBrussels.^[57] Among other examples, this can be seen on the street façade of theCauchie House.^[58]

Wikimedia Commons has media related toHorseshoe arches.

• Arches and vaults
• Islamic architectural elements
• Iranian architectural elements

• CS1 maint: multiple names: authors list
• CS1 maint: publisher location
• CS1 French-language sources (fr)
• Articles with short description
• Short description matches Wikidata
• Articles containing Arabic-language text
• Articles containing Spanish-language text
• Commons category link is on Wikidata