Moorish architecture partially coincident with Art of Al-Andalus
The Hammadids, an offshoot of the Zirids, ruled in the central Maghreb (present-day Algeria) during the 11th and 12th centuries. They built an entirely new fortified capital known as Qal'at Bani Hammad, founded in 1007. Although abandoned and destroyed in the 12th century, the city has been excavated by modern archeologists and the site is one of the best-preserved medieval Islamic capitals in the world. It contains several palaces, various amenities, and a grand mosque, in an arrangement that bears similarities to other palace-cities such as Madinat al-Zahra.: 125–126 : 88–93  The largest palace, Qasr al-Bahr ("Palace of the Sea"), was built around an enormous rectangular water basin. The architecture of the site has been compared to Fatimid architecture, but bears specific resemblances to contemporary architecture in the western Maghreb, Al-Andalus, and Arab-Norman Sicily. For example, while the Fatimids usually built no minarets, the grand mosque of Qal'at Bani Hammad has a large square-based minaret with interlacing and polylobed arch decoration, which are features of architecture in al-Andalus.: 88–93  Various remnants of tile decoration have been discovered at the site, including the earliest known use of glazed tile decoration in western Islamic architecture.: 91–93  Archeologists also discovered fragments of plaster which have been identified by some as the earliest appearance of muqarnas ("stalactite" or "honeycomb" sculpting) in the western Islamic world,: 133  but their identification as true muqarnas has been questioned or rejected by some other scholars.: 93Arches
Horseshoe arch
Perhaps the most characteristic arch type of western Islamic architecture generally is the so-called "Moorish" or "horseshoe" arch. This is an arch where the curves of the arch continue downward past the horizontal middle axis of the circle and begin to curve towards each other, rather than just forming a half circle.: 15  This arch profile became nearly ubiquitous in the region from the very beginning of the Islamic period.: 45  The origin of this arch appear to date back to the preceding Byzantine period across the Mediterranean, as versions of it appear in Byzantine-era buildings in Cappadocia, Armenia, and Syria. They also appear frequently in Visigothic churches in the Iberian peninsula (5th–7th centuries). Perhaps due to this Visigothic influence, horseshoe arches were particularly predominant afterwards in al-Andalus under the Umayyads of Cordoba, although the "Moorish" arch was of a slightly different and more sophisticated form than the Visigothic arch.: 163–164 : 43  Arches were not only used for supporting the weight of the structure above them. Blind arches and arched niches were also used as decorative elements. The mihrab of a mosque was almost invariably in the shape of horseshoe arch.: 164 Starting in the Almoravid period, the first pointed or "broken" horseshoe arches began to appear in the region and became more widespread during the Almohad period. This arch is likely of North African origin, since pointed arches were already present in earlier Fatimid architecture further east.: 234
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