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Hagia Sophia Dome: Construction & Design

Instructor: David Juliao

David has a bachelor's degree in architecture, has done research in architecture, arts and design and has worked in the field for several years.

In this lesson, learn about the characteristics of one of the most important architectural achievements of all time: the Hagia Sophia dome. Explore the design and construction of this masterpiece, including its key structural elements.

Hagia Sophia in Istanbul

Istanbul is an enigmatic city where Asia meets Europe, and it has seen many empires rise and fall. In the heart of the city lies its most distinctive landmark, the Hagia Sophia, which means Holy Wisdom. This marvelous construction has crowned the city's skyline for almost 1,500 years. Let's find out more.

Hagia Sophia in Istanbul
Hagia Sophia in Istanbul

Hagia Sophia is a religious building in Istanbul, Turkey, considered to be one of the most relevant monuments of architecture from the Eastern Roman Empire, also known as Byzantine architecture. The building is most famous for its massive dome and for having relics such as nails from Jesus' True Cross and the Shroud of Mary, which were taken during the Middle Ages by the Crusaders.

Byzantine Emperor Justinian I ordered the cathedral's construction in response to the destruction by rioters of two buildings that existed there before. The construction started in the year 532 AD and was finished in 537.

The building served as an Orthodox Christian church from 537 until 1453, except for a few decades in the 13th century when it was adapted to be a Catholic cathedral by the Crusaders. In 1453, it was then converted into a mosque when Istanbul was added to the Ottoman Empire, a long-lasting realm that occupied the territories of today's Turkey. In 1935, it was finally transformed into a museum, which continues to be visited today.

Characteristics of Hagia Sophia's Dome

One of the problems with the original dome was its weight, and that caused it to collapse completely after a series of earthquakes in the year 558. Isidore the Younger was commissioned to do the reconstruction. He used lighter materials, made structural improvements, and incorporated constructive elements that gave the dome its current aspect and dimensions.

Use of Mortar and Brick

The construction was made using brick and mortar as the main materials for the dome. More mortar than brick was used, however, and builders didn't let the mortar dry properly before starting a new layer. That weakened the walls, causing them to lean. When Isidore started the reconstruction, he had to rebuild all the interior walls first to make them vertical and strong enough to support the weight of the new dome.

The Square Base

The geometry of Hagia Sophia is based on a Greek cross layout, inscribed in a square box. The area in the center of this cross is the room of the square base that supports the dome. This base isn't actually perfectly straight; it curves into the dome, helping to support it while also allowing the weight to flow downwards and cause less tension on the structure.

Pendentives to Support the Dome

One of the constructive improvements introduced was the use of pendentives. These elements in the form of spherical triangles are a structural transition between the square shape of the base and the round shape of the dome. They help to transfer the loads from the dome, down to the base walls, and finally onto the ground.

Section drawing of the Hagia Sophia dome
Section drawing of Hagia Sophia Dome

The Hagia Sophia dome is supported by four pendentives that were built at each corner of the square base of the cathedral. The use of pendentives by Isidore marked the first large-scale incorporation of this constructive element, which became distinctive of Byzantine architecture. These constructive elements were reinforced in later centuries, using large buttresses. In total, 24 buttresses were built to strengthen and support the four pendentives.

The Form of a Scalloped Shell

After the reconstruction made by Isidore, the new cupola was given the shape of a scalloped shell, or the inside of an umbrella, by using ribs that extended from the top to the base. These reinforcements not only made the dome stronger, but they also allowed for the weight to be distributed more efficiently.

Lighting effects

One of the most famous aspects of the Hagia Sophia is the lighting effects created in the interior, and how sunlight reflects on the inside, giving the dome the illusion of hovering above. To achieve this, 40 windows were built on the original structure. Furthermore, the insertion of those windows on the dome also helps to lower its weight, so the windows are part of the structural solution as well.

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