Hagia Sophia's architecture: Grand Dome, intricate mosaics, & tall columns

Anthemius was born in Tralles, a city in Asia Minor, and played a key role in devising the innovative architectural solutions that enabled the construction of the Hagia Sophia's massive dome. His understanding of geometry and mechanics helped builders overcome technical challenges and create a series of arches and semi-domes to support the imposing dome.

Isidore, hailing from the city of Miletus, was a skilled architect and mathematician. He collaborated closely with Anthemius and conceptualized the overall architectural plan of the Hagia Sophia, including its distinctive dome and innovative structural features. Isidore's meticulous attention to detail and his understanding of architectural aesthetics helped to shape the Hagia Sophia into a masterpiece of Byzantine architecture.

Over time, the Hagia Sophia has undergone many changes. A major renovation was carried out in the 10th Century by Emperor Basil II. He restored the collapsed dome of the church and installed four large murals of cherubim, a new representation of Christ on the vault, a burial cloth of Christ, and on the apse, a new representation of the Virgin Mary cradling Jesus, among the apostles, Peter and Paul.

As a mosque under the Ottomans, a small minaret was added in the southwest corner of the Hagia Sophia Mosque. A widespread renovation of the Hagia Sophia Mosque was ordered by Sultan Abdulmejid I in 1847. Gaspare and Giuseppe Fossati, two Swiss-Italian architects, supervised the straightening of some columns, the securing of the vaults, the consolidation of the dome, and the redecoration of the mosque's exterior and interior. A new maqsurah was added to the northern aisle of the Mosque of Hagia Sophia in 1850.

Since the Hagia Sophia was built on a fault line, every earthquake in the region wreaked havoc on its foundation. Its condition continued to deteriorate and Hagia Sophia was listed on World Monuments Watch in 1996 and again in 1998 by the World Monuments Fund (WMF). The first stage of work, with the Turkish Ministry of Culture, was to stabilize the cracked roof. By 2006, the WMF project was complete, although many other parts of the Hagia Sophia still need substantial improvements.

The minarets were an Ottoman addition and not part of the original Byzantine church. The southeast minaret was constructed with red brick and can be dated back to the reign of Mehmed or his successor Beyazıd II. The other three were constructed with white limestone and sandstone, of which Bayezid II erected the slender northeast column and Selim II erected the two identical larger minarets to the west.

The iconic Hagia Sophia dome can be instantly spotted from a distance. It has a diameter of around 31 meters. Four spherical triangular pendentives bear the dome. The pendentives are the corners of the dome's square base, curving upwards into the dome to support it, restricting the dome's lateral forces and allowing its weight to flow downwards. The dome was left somewhat elliptical due to repairs.

Hagia Sophia has mosaics on the inside of its dome, the imperial gate, the southwestern gate, as well as the northern tympanum. However, the most significant of them are the mosaics on the apse. Mary, the mother of Jesus carrying the Christ Child and sitting on a jeweled thokos backless throne, is shown in the mosaic in the semi-dome above the apse on the east end. It is not known when the mosaic was installed.