Editing Hagia Sophia (section)

===Dome===
[[File:Istanbul asv2021-10 img22 Hagia Sophia.jpg|thumb|View of the dome interior]]

The [[dome]] of Hagia Sophia has spurred particular interest for many art historians, architects, and engineers because of the innovative way the original architects envisioned it. The dome is carried on four spherical triangular [[pendentive]]s, making the Hagia Sophia one of the first large-scale uses of this element. The pendentives are the corners of the square base of the dome, and they curve upwards into the dome to support it, thus restraining the lateral forces of the dome and allowing its weight to flow downwards.<ref>Kleiner and Mamiya. ''Gardner's Art Through the Ages'', p. 331.</ref><ref>{{cite encyclopedia |url=https://www.britannica.com/EBchecked/topic/449698/pendentive |title=pendentive (architecture) – Britannica Online Encyclopedia |encyclopedia=Britannica.com |access-date=4 December 2011}}</ref> The main dome of the Hagia Sophia was the largest pendentive dome in the world until the completion of [[St Peter's Basilica]], and it has a much lower height than any other dome of such a large diameter.

The great dome at the Hagia Sophia is {{convert|32.6|m}} in diameter and is only {{convert|0.61|m}} thick. The main building materials for the original Hagia Sophia were brick and mortar. Brick aggregate was used to make roofs easier to construct. Due to the material's plasticity, it was chosen over cut stone due to the fact that aggregate can be used over a longer distance.<ref>{{Cite journal |last=MacDonald |first=William |date=1957 |title=Design and Technology in Hagia Sophia |journal=Perspecta |volume=4 |pages=20–27 |doi=10.2307/1566853 |issn=0079-0958 |jstor=1566853}}</ref> According to Rowland Mainstone, "it is unlikely that the vaulting-shell is anywhere more than one normal brick in thickness".<ref>{{Cite book |last=Mainstone |first=Rowland J. |url=https://books.google.com/books?id=jSw7FSSrd8AC |title=Hagia Sophia: Architecture, Structure, and Liturgy of Justinian's Great Church |date=1997 |publisher=Thames and Hudson |isbn=978-0-500-27945-8 |pages=81 |language=en}}</ref>

The weight of the dome remained a problem for most of the building's existence. The original cupola collapsed entirely after the earthquake of 558; in 563 a new dome was built by [[Isidore the Younger]]. Unlike the original, this included 40 ribs and was raised 6.1 meters (20 feet), in order to lower the lateral forces on the church walls. A larger section of the second dome collapsed as well, over two episodes, so that as of 2021, only two sections of the present dome, the north and south sides, are from the 562 reconstructions. Of the whole dome's 40 ribs, the surviving north section contains eight ribs, while the south section includes six ribs.<ref>{{cite book |last=Mainstone |first=Rowland J. |title=Hagia Sophia |year=2001 |publisher=Thames & Hudson |location=London |isbn=978-0-500-27945-8 |pages=90–93}}</ref>

Although this design stabilizes the dome and the surrounding walls and arches, the actual construction of the walls of Hagia Sophia weakened the overall structure. The [[bricklayer]]s used more [[Mortar (masonry)|mortar]] than brick, which is more effective if the mortar was allowed to settle, as the building would have been more flexible; however, the builders did not allow the mortar to cure before they began the next layer. When the dome was erected, its weight caused the walls to lean outward because of the wet mortar underneath. When Isidore the Younger rebuilt the fallen cupola, he had first to build up the interior of the walls to make them vertical again. Additionally, the architect raised the height of the rebuilt dome by approximately {{cvt|6|metres|feet}} so that the lateral forces would not be as strong and its weight would be transmitted more effectively down into the walls. Moreover, he shaped the new cupola like a [[scallop]]ed shell or the inside of an umbrella, with [[Ogival arch|ribs]] that extend from the top down to the base. These ribs allow the weight of the dome to flow between the windows, down the pendentives, and ultimately to the foundation.<ref name="Mainstone-1988">{{Cite book |title=Hagia Sophia: Architecture, structure, and liturgy of Justinian's great church |last=Mainstone |first=R.J. (Rowland J.) |date=1988 |publisher=Thames and Hudson |isbn=978-0-500-34098-1 |location=New York |oclc=15378795}}</ref>

Hagia Sophia is famous for the light that reflects everywhere in the interior of the nave, giving the dome the appearance of hovering. This effect was achieved by inserting forty windows around the base of the original structure, which also reduced its weight.<ref name="Mainstone-1988" />