Hagia Sophia's extreme engineering design and structural innovations

Hagia Sophia

The Triumph of Balance:

Structural Engineering in the Hagia Sophia

When the Basilica of Hagia Sophia was dedicated on December 27, 537, it stood as a towering monument not only to Christianity, but to the strength and power of the empire, and emperor, that made it possible. The spectacular columns and marbles that adorned it had been brought in from as far away as the Aegean and even the west coast of France (Krautheimer 205). Detailed mosaics celebrating the power and piety of Justinian adorned its walls. Upon seeing its finished form, the emperor is reputed to have said, "Solomon, I have vanquished thee," implying that the Basilica outshone even the glories of Solomon's temple in Jerusalem (Krautheimer 206).

Since then, the "Great Church" (as it would come to be known in the Middle Ages) has captivated people of all faiths, despite its many alterations and transformations. The cathedral as it stands today bears the marks not only of its original splendor but of the political and religious changes that surrounded it in the centuries after its completion. Fergus Bordewich, in an article for Smithsonian Magazine, called the current structure "a complex accretion of myth, symbol and history" (2). That it still stands, despite the societal turmoil and natural disasters that have threatened and continue to threaten it, is a testament to the intelligence and care that lay behind its construction.

It was of great political importance for Justinian to build not just an impressive structure, but a structure designed to resist destruction. He built the basilica to replace a previous Hagia Sophia that had been built on the same site by Constantine II. This structure had been burned to the ground by the populace of Constantinople during the Nika rebellion of 532, when the people rose up against overtaxing by Justinian. The rebellion very nearly ended Justinian's rule; only his wife's refusal to abandon her throne convinced him to crush the rebellion. He triumphed, leaving over 30,000 dead in the streets, but not before the original Hagia Sophia lay in ashes (Salvadori et al. 247). Justinian decided to rebuild, not only to replace the house of worship, but to leave a lasting reminder of his position "as a ruler with the stamp of divine authority" ("Fabled Sanctuary" 1).

He could not trust this most important endeavor to just any master builder. His desire for a building beyond what had been built before, both in beauty and in engineering, meant that he need someone accomplished not only in design but also in physics and mathematics. He found this combination in Anthemios of Tralles and his assistant Isidorus of Miletus. These architects were what were known as mechanopoioi, designers who were well-trained in kinetics, physics, and mathematics (Krautheimer 206). Their background in theoretical engineering made them not only willing but also qualified to take the structure of the Hagia Sophia "to the very limits of…safety coefficients" (Krautheimer 207). They were not altogether successful in their revolutionary design. The original dome collapsed within a quarter century, and the buttresses had to be reinforced several times throughout the following centuries (Ibid). But the audaciousness and simplicity of their original design remains.

The defining feature and in many ways the most impressive engineering marvel of the Hagia Sophia is the great dome that dominates its center. The dome rises forty-five feet above the square of four pillars that supports it. The four pillars are connected by full arches, and upon these arches rests a horizontal circle that supports the dome itself. Forty windows sit at the base of the dome, separated by the forty ribs that provided support for the original dome (Salvadori et al. 252). It is this ring of windows that gives the dome the celebrated appearance of floating. Procopius, a 6th-century historian, noted that the dome "does not appear to rest upon a solid foundation, but to cover the place beneath as though it were suspended from heaven by the fabled golden chain" (qtd. In Bordewich 2).

The northern and southern arches that support the dome are themselves supported by walls and a series of marble columns. The walls contain three rows of windows (though the bottom row was later plugged up), giving the entire space a light, iridescent appearance. The eastern and western dome arches are not filled by walls, but are flanked by a series of half-domes. These half-domes are supported by pillars and columns set in semi-circles. Leading out from the northern and southern walls are aisles created by rows of columns and barrels vaults. The entire structure is encompassed by an outside wall. (Salvadori et al. 253)

Much of the structure's strength is due to its material. With the burning of the previous church still fresh in his mind, Justinian was insistent that his church be fireproof (Salvadori et al. 254). Anthemios therefore relied on granite and marble as his principal building materials for the base of the church. He knew that the weight of the domes on the supporting arches and columns would be enormous, so he took great pains to ensure that this weight would be evenly distributed by making the surfaces of the granite blocks absolutely even and using lead sheet between important joints to ensure complete contact (Ibid).

Anthemios knew, however, that he had to balance the brute strength of the base of the building with lighter materials in the upper structure. Therefore, he used bricks for the dome, half-domes, and vaults. These bricks measured only two inches thick, and were placed at an angle in limestone mortar that dried to the same hardness as the brick, creating a light, strong, and practically homogenous material (Krautheimer 212). Though the domes have suffered partial collapses and repairs throughout the centuries, the fact that they have remained relatively intact is a testament to Anthemios' thoughtful application of mechanics.

That the whole structure still remains is, in the words of Richard Krautheimer and others, a "sheer miracle" (212). There have been many threats to its existence -- both natural and man-made. The whole structure sits on top of a geographic fault line, and has experienced innumerable earthquakes in its 1500-year history. Architect and engineer Stephen Kelley sees every earthquake as potentially devastating for the basilica: "One tremor and the whole thing could come falling down" (qtd. In Bordewich 2). Why, after surviving over a millenium's worth of tremors, is it particularly vulnerable now? Its longevity, suggests Kelley, is part of its weakness. The many repairs and alterations to it over the centuries have compromised the unity of the building. "[I]n an earthquake," he points out, "unless a building acts as a single tightly connected unit, its parts will work against each other" (Ibid).

It is not only the building's structure that is at risk. The Hagia Sophia, beyond being an engineering marvel, is one of the world's great historical and artistic treasures. After centuries of utilitarian appreciation as an important place of worship, first as a Christian church and then a Muslim mosque, the Hagia Sophia began to be acknowledged in the 19th and 20th centuries as "a great monument of world art" (Nelson xv-xvi). So striking were the Christian mosaics on the walls of the church that 19th-century Sultan Abdulmecid, despite his acknowledgement that they were no longer appropriate in what was now a mosque, insisted that they be covered in a way "that they may survive until they are revealed to view in the future" (qtd. In "Fabled Sanctuary" 1). Its importance as a cultural treasure was sealed in 1934, when the great Turkish leader Mustafa Kemal Ataturk retired the building as a mosque and established it instead as a museum (Ibid).