< ">The Hagia Sophia has a classical basilica plan. The main ground plan of the building is a rectangle, 230 feet (70 m) in width and 246 feet (75 m) in length. The area is covered by a central dome (see outside and inside) with a diameter of 102 feet (31 m), which is just slightly smaller than that of the Pantheon in Rome.
The main dome is carried on pendentives: four concave triangular sections of masonry which solve the problem of setting the circular base of a dome on a rectangular base. Each pendentive is decorated with a seraphim. The weight of the dome passes through the pendentives to four massive piers at the corners, and between them the dome seems to float upon four great arches.
At the western and eastern ends, the arched openings are extended by semi-domes. The flat wall on each side of the interior (north and south) is called a tympanum, and each one has 12 large windows in two rows, seven in the lower and five in the upper.
Just outside the entrance, stone cannonballs line the gravel path of the outer courtyard. These are the actual cannonballs used by Mehmet the Conqueror in his victorious 1453 battle for the city.
All interior surfaces are sheathed with polychrome marble, green and white with purple porphyry, and gold mosaics. On the exterior, simple stuccoed walls reveal the clarity of massed vaults and domes.
The Islamic calligraphic roundels suspended from the main dome since the 19th century remain in place and make for a fascinating religious contrast with the uncovered Christian mosaics. The names painted on the eight wooden medallions are: Allah and Muhammad (flanking the apse); the first four Caliphs Abu Bakr, Umar, Uthman and Ali (at the four corners of the dome); and the two grandsons of Mohammed, Hasan and Husayn (in the nave).
When the Hagia Sophia was used as a place of worship, both for Christians and then for Muslims, the focus of the building was the east end, directly across from the entrance. This is because Christian churches are traditionally oriented towards the east, and Muslims always pray facing Mecca, which is southeast of Istanbul (the "east" end of the Hagia Sophia actually faces southeast). Thus the bulk of interesting sights are clustered in this area of the Hagia Sophia's huge interior.
At ground level, most of the sights date from the Islamic period. A beautiful marble structure in the apse is the mihrab, a niche found in all mosques that indicates the direction of Mecca. The large freestanding stairway to the right of the mihrab is the minbar, or pulpit from which sermons were given. To the left of the mihrab is the grand sultan's loge, built by the Fossati brothers who restored the Hagia Sophia in the 1800s.
Looking up from this area, one sees a splendid apse mosaic depicting the Virgin and Child. On the right is a partly damaged Archangel Gabriel mosaic. Gabriel used to face an Archangel Michael mosaic on the other side of the apse, but this is now almost entirely gone.
The most famous of the Hagia Sophia's mosaics are on the upper floor, in the galleries. The South Gallery, where the great mosaics are, was used for church councils. When the Hagia Sophia was a mosque, the galleries were the place where women sat during worship services. Today, the galleries provide visitors with a commanding view of the nave from all sides and a closeup view of some of the best Byzantine mosaics to be seen anywhere.
The best-known mosaic is called the Deësis Mosaic, and it is the first you come to as you enter the South Gallery through the Marble Door. It depicts a triumphant and kingly Christ (known as "Christ Pantrocrator"), flanked by the Virgin Mary and John the Baptist.
The modern exit from the Hagia Sophia is through the Vestibule of the Warriors, so called because it is where the emperor's bodyguards waited while he worshipped. Up high and behind you as you walk out is a splendid mosaic of the Virgin with Constantine and Justinian: Constantine the Great presents to the Virgin a model of the city of Constantinople (Istanbul), which he founded, and Emperor Justinian presents the church of the Hagia Sophia, which he rebuilt. This mosaic dates probably from the 10th century.
There are several interesting things to see outside Hagia Sophia, including three mausoleums of sultans, the church's baptistery, and the excavated remains of Theodosius' Hagia Sophia.