Hagia Sophia

What is Hagia Sophia?
Hagia Sophia is a monumental domed building in Istanbul that has served in succession as an Eastern Orthodox cathedral, a Roman Catholic cathedral, an Ottoman mosque, a secular museum, and once again a mosque, across nearly fifteen centuries of continuous use. Completed in 537 under the Byzantine emperor Justinian I, it was for centuries the largest cathedral in the Christian world and remains one of the most influential buildings in the entire history of architecture. Few structures anywhere have changed religious hands so many times while remaining in continuous active use.

What stood on the site before the current building?
The site had already hosted two earlier churches before Justinian's version was built, beginning with a structure dedicated in the fourth century under Emperor Constantius II. This first church burned down during civil unrest in 404, and its replacement stood for over a century before it too was destroyed, this time during the violent Nika riots that swept through Constantinople in 532. Justinian used the destruction of this second church as the opportunity to commission something far grander than either of its predecessors.

Why did Justinian commission this version, and how quickly was it built?
Justinian assigned the project to two mathematicians rather than conventional architects, Isidore of Miletus and Anthemius of Tralles, whose combined expertise in geometry and engineering shaped the building's revolutionary design. Remarkably, construction proceeded from 532 to 537, meaning the entire structure was completed in under six years despite its unprecedented scale and ambition. According to tradition, Justinian entered the finished building and declared that he had surpassed the biblical King Solomon, a boast that captured both his pride and the genuine originality of what had been achieved.

What made its dome such an architectural achievement? Hagia Sophia's central dome rested on pendentives, a then-innovative architectural technique that allowed a circular dome to be supported cleanly atop a square base, a solution few if any earlier builders had successfully achieved at this scale. The completed building became the largest interior space in the world at the time, a status it held for centuries, and its dome remains widely regarded as one of the defining engineering achievements of Late Antiquity. This combination of mathematical precision and sheer visual drama gave the building an impact contemporaries described as genuinely transformative.

What happened when the original dome partially collapsed?
An earthquake in the following decades caused significant damage to the original, relatively shallow dome, leading to a partial collapse that required extensive rebuilding. The replacement dome, constructed with a somewhat steeper profile intended to better withstand future seismic stress, was completed under the direction of Isidore the Younger, nephew of one of the original architects. This successful reconstruction ensured the building's central feature would endure for the many centuries that followed.

How did the building's religious status shift during the Byzantine period?
Hagia Sophia served as the principal cathedral of Eastern Orthodox Christianity for roughly six and a half centuries, hosting imperial coronations and standing at the very centre of Byzantine religious and political life. This continuity was interrupted in 1204, when the Fourth Crusade captured Constantinople and converted the building to Roman Catholic use under the short-lived Latin Empire that followed. Byzantine forces recaptured the city in 1261, restoring Hagia Sophia to Eastern Orthodox use for nearly two more centuries until the empire's final collapse.

What happened when the Ottomans conquered Constantinople in 1453?
Following the Ottoman conquest under Sultan Mehmed II, Hagia Sophia was promptly converted into an imperial mosque, a transformation that likely spared the building from the kind of destruction inflicted on other captured structures. Successive sultans added minarets gradually over the following century and a half, including a pair designed by the celebrated Ottoman architect Sinan, along with a mihrab, a minbar, and other features required for Islamic worship. The building would go on to function as a mosque for nearly five hundred years under Ottoman rule.

What happened to the building's Christian imagery?
Many of Hagia Sophia's original figurative religious images had already been removed or destroyed centuries earlier during the Byzantine Iconoclasm controversies of the eighth and ninth centuries, meaning the mosaics that survive today largely postdate that upheaval. Following the Ottoman conversion, most remaining Christian mosaics were plastered over rather than destroyed outright, a practice consistent with Islamic conventions regarding figurative imagery in places of worship. This plastering inadvertently preserved many of these artworks, allowing later restorers to rediscover and reveal them centuries afterward.

How did it become a museum in 1934?
Mustafa Kemal Atatürk, founder of the modern Turkish Republic, secularised Hagia Sophia by decree in 1934 as part of his broader programme of reforms separating religion from the new state's public institutions. The building opened formally as a museum the following year, allowing extensive restoration work that uncovered and displayed many of the Byzantine mosaics that had remained hidden beneath Ottoman-era plaster for centuries. Hagia Sophia was later included within the UNESCO World Heritage listing for the Historic Areas of Istanbul in 1985, formally recognising its exceptional global significance.

What happened when it was reconverted to a mosque in 2020?
In July 2020, a Turkish court annulled Atatürk's 1934 secularisation decree, and President Recep Tayyip Erdoğan subsequently ordered Hagia Sophia's reconversion into a functioning mosque, ending eighty-five years of operation as a secular museum. The decision drew significant international criticism, including formal objections from Greece, statements of concern from Eastern Orthodox Christian leaders, and warnings from heritage historians about the implications for a UNESCO-listed site of such singular cultural importance. Despite the change in official status, the building has remained open to visitors of all backgrounds, continuing to draw enormous numbers of tourists alongside worshippers.

Why does it deserve a card?
Hagia Sophia has functioned as a cathedral, a mosque, a museum, and a mosque once again, absorbing nearly fifteen centuries of religious and political upheaval while remaining one of the most technically astonishing buildings ever constructed. Its dome solved an engineering problem that had defeated earlier architects, its walls carry the physical traces of Christian and Islamic worship layered directly atop one another, and its ownership remains a genuinely contested question even today. Few buildings anywhere on earth compress so much of human history, faith, and architectural ambition into a single continuously occupied structure.

The Hagia Sophia is part of Volume III

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