Ablaq
Ablaq (; particolored; literally 'piebald') is an architectural technique involving alternating or fluctuating rows of light and dark stone. It is an Arabic term describing a technique associated with Islamic architecture in the Arab world. It may have its origins in earlier Byzantine architecture in the region, where alternating layers of white stone and orange brick were used in construction. The technique is used primarily for decorative effect. Origins 
The ablaq decorative technique is thought to maybe be a derivative from the ancient Byzantine Empire, whose architecture used alternate sequential runs of light colored ashlar stone and darker colored orange brick. The first clearly recorded use of ablaq masonry is found in repairs to the north wall of the Great Mosque of Damascus in 1109. The technique may have originated in Syria, where the local stone supply may have encouraged the use of alternating courses of light and dark stone. In the southern part of Syria there is abundance of black basalt as well as white-colored limestone. The supplies of each are about equal, so it was natural that masonry techniques of balanced proportions were used. Use in Islamic architecture 

The Dome of the Rock in Jerusalem, originally built in the late 7th century during the Umayyad period, features ablaq light and dark stone voussoirs in the arches of its inner colonnade. The origins of the marble ablaq treatments at the Dome of the Rock are controversial, with some scholars theorizing them to be from the original construction, and some saying they were later additions (and differing then as to the dates and identity of the builders). The alternating red and white masonry in the voussoirs of arches at the Great Mosque of Córdoba – built in the late 8th century and expanded up to the 10th century – is another early example of such a technique, which could be related to earlier examples in Jerusalem and Damascus that the Umayyad rulers of Córdoba were familiar with. Andrew Petersen, a scholar of Islamic art and archeology, states that ablaq (alternating courses of white limestone and black basalt) is "a characteristic of the monumental masonry of Damascus." Ablaq masonry appears in some 12th and 13th-century buildings in Diyarbakir built under the Artuqids, as well as in some late Ayyubid buildings in Damascus. It also appears in the portals of some 13th-century Seljuk monuments in Konya, such as the Alaeddin Mosque the Karatay Madrasa, possibly due to the influence of Syrian craftsmen. Ablaq became a prominent feature of Mamluk architecture in Syria, Egypt and Palestine in the 14th and 15th centuries. During this period, black and white stone were often used as well as red brick in recurring rows, giving a three colored striped building. Ablaq masonry supplemented other decorative techniques such as the use of "joggled" voussoirs in arches, where stones of alternating colours were cut into interlocking shapes. In 1266 the Mamluk sultan al-Zahir Baybars al-Bunduqdari built a palace in Damascus known as the  ("Ablaq Palace"), which was constructed with alterations of light and dark masonry. This name shows that the term ablaq was in regular usage for this type of masonry in the 13th century. In Jordan, the Mamluk fortified khan at Aqaba is a medieval fortress modeled after those used by the Crusaders. It contains an arch above the protected entrance. The horseshoe arch has ablaq masonry, harkening to Mamluk architecture in Egypt.Construction with alternating layers of brick and stone was often used in early Ottoman architecture in Anatolia and the Balkans, but it fell out of fashion in later Ottoman imperial architecture. The traditional ablaq technique continued to be used regionally in the architecture of Ottoman Syria (16th century and after). Examples in Damascus include the Sulaymaniyya Takiyya (16th century), the Azm Palace (18th century), and the Khan As'ad Pasha (18th century). Use in Christian Europe 

The technique of alternating light and dark stone constructions also appeared in Christian Europe around the mid 12th century, but it is uncertain whether this development occurred independently or was influenced by existing examples in Syria. Notable examples include the 13th-century cathedrals of Monza, Siena, and Orvieto, as well as a palace in Genoa. Pisan ecclesiastical monuments—particularly the Cathedral of Pisa and Church of San Sepolcro (commenced building 1113)—used ablaq, not simple "black and white in revetment" between the conquest of Jerusalem in the First Crusade (1099) and the completion of the latter ca. 1130. Various architectural motifs—ablaq, the zigzag arch, and voussoir (rippled and plain) were used. According to scholar Terry Allen, these embellishments were a direct appropriation of Muslim architecture, resulting from pilgrimage to Jerusalem and the wars in the Levant from resulting from the First Crusade. Visitors to Jerusalem could see ablaq at the Dome of the Rock and at the Church of the Holy Sepulchre, as well as other examples that may no longer be extant. Thus zigzags and ablaq became part of the repertoire of Romanesque architecture. References

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Further reading 

Arches and vaults
Architecture in Syria
Byzantine architecture
Arabic architecture
Islamic architectural elements
Mamluk architecture
Masonry
Moorish architecture
Ottoman architecture
Ornaments (architecture)
Architecture in Lebanon
Architecture in the State of Palestine
Architecture in Jordan
Architecture in Egypt