Today, after repeated restoration and ad­ditions, the Hagia Sophia is notably altered. Several earthquakes damaged the þtructure and in 558 A.D. the dome partially collapsed. This was rebuilt by the young Isidoros, when the dome was rais­ed by 6.25 ms., and reopened in 562 A.D. Later repairs failed to provide the building with the static support essential for its stability. Repeated earthquakes continued to weaken the fabric and the cost of maintainance ro se continuously. During the Latin invasion, the LV crusaders sacked and damaged Hagia Sophia, as if it were a pagan temple, in 1204. The gilded silver panels flanking the Imperial portal were taken as booty by crusading soldiers, along with gold and silver erosses and any available valuables, while crusading monks acquired what religious artefacts they could, inflicting the greatest damage ever suffered by the cathedral throughout history.

When the city was recaptured by the Paleologs in 1261, the emperor Michael VIII (1261-1282) ordered the restoration of the church by the monk and architect Ruchas. The buttress walls on the western facade date from this period. Pyramidal buttresses were added to the northern and southern walls in 1317 to offset the effect of the dome's weight which was pushing out the walls. This addition dates from the reign of Andronicus II.

On the Turkish conquest of Istanbul in 1453, Mehmet II found the church in a state of ruin. The conqueror le ad the first Friday prayers there and ordered it to be converted into a mosque. Later a mihrab was added to the eastern apse in line with the qibla - facing towards Mecca, and a wooden minaret was erected over one of the western cupolas. The main structure and mosaics on the interior were left un­touched. Later, during the period of Süleyman i (1520- 1566) the mosaics were plastered over. The' brick minaret on the south-eastern flank and a buttress wall on the eastern facade were added ear1ier, during the reign of Mehmet n. The slimmer minaret on the north-eastern flank was' added during the reign of Bayezid n (1481-1512), while the two more solid minarets to the west were ad­ditions of the Selim n (1566- 1574) period, and were constructed by the architect Sinan.

The Ottoman sultans restore d and main­tained the building in the best possible state, embellishing it ,with Islamic works of art. A muezzin's gallery in fine relief marble was added to the furniture of the mosque during the reign of Murat ný (1574-1595). Two marble amphorae dating from the Hellenistic period were brought from Bergama and set up to either side of the portal on the interior, which, with the addition of faucets, were used for ritual washing before prayer. T wo large candelabrae flanking the mihrab were among the spoils of Budin,captured by Süleyman i during his Hungarian campaign. A marble mimber and the rnarble pulpit set to the left of the space under the main dome were add­ed during the reign of Murat iV (1623- 1640). A library adjoining the mosque was added during the reign of Mahmut i. Finely decorated with ýznik tiles, it contained space for 30. ()OO books. During the same period a fountain - one of the finest ip Turkish architecture - was erected in the mosque court. together with a school and observatory. Four sultan's mausoleums are to be found in the eastern corner of the gardens which also contain the Baptistry, later converted into a mausoleum.

The most extensive restoration to the fabric of Hagia Sophia took place dur­ing the f<3ign of Abdülmecit (1847- ). Under the direction of the Italian architect Gaspar Fossati, the dome was stabilised by the addition of a double iron band clamped around it. The roof was relead­ed and columns moving out of true were restored. The mosaics were uncovered and restored, those with cruciform pat­terns and human figures replastered, while the imperial gaIlery was given its present day appearance by Fossati. The restorations took two years.

The large inscription plaques, 7.5 ms. in diameter were attached to the waIls at that time. They were the work of the caIligrapher Hattat Izzet Efendi, who also decorated the dome with his inscription of verses from the Kor'an.

Haghia Sophia was decIared a national monument and became a museum by ord er of Atatürk on 24 October, 1934.

The church is entered via the western portal whieh leads into the Exonarthex, from which five portals open into the Narthex (11 x 60 ms.), notable for the polychrome marble revetments.

The narthex opens into the main body of the church through nine portals, the three central portals being the Imperial Door5. Over the main portal is a mosaie of Christ enthroned dated to the 9th century. The figure of Christ has his right hand raised in blessing, while his left hand holds up a book resting on his knee. The mosaie is fIanked to right and left by the figures of the Blessed Virgin and the angel Gabriel in roundels. Prostrated before the throne is the figure of Leo Vi (886-912 A.D.).

The total area of the church ihcIuding its narthexes is 7570 m2. it is the fourth largest church in the world. The interior is do~inated by a dome 55.60 m2 in height. The dome is not quite circular, measuring 30.8 m. x 31.88 m., and rests on four main. piers joined by four supporting arches. The drum is pierced by forty windows. Of the surviving decoration, the Cherubim in the pendentlves are frescos dating to the 10th century. The mosaie of the Mother of God enthroned, bearing the Christ child in the apse dates to the 9th century. The figure of the Madonna (Theodokos Madonna) is of idealised beauty.

Set within blind niches along the north waIl are the mosaie portraits of three beatified members of the Ichurch cIergy, the Patriarch of Constantinople, lohannes Khrysostomos, the archbishop of Antalya, Ignatios and St. Ignatios Theophoros, in frontal pose against a gold ground.

In the northern nave is the so-caIled "sweating column", of pourous marble whieh absorbed water froma cistern below. The damp absorbed by the column can be felt by placing the hand in a hole in the" shaft whieh has been worn into it and is framed in bronze. Even in Byzantine times this piIler was considered miraculous.

At the south of the central nave is an area of marble mosaie of extremely fine quality. This is believed to be the spot upon whieh the Byzantine emperors were crowned, and was known as the Byzantine omphalos (centre of the earth). The church is surrounded on three sides by gaIleries, there being no gaIlery over the apse. The gaIleries have finely decorated ceilings and contain some mosaies of considerable value.

The Deesis mosaie in the south gallery is dated to the 12th century. it is partiaIly destroyed, but stili the fine and delicate, workmanship of the mosaie can be easily seen in a work of partieularly smaIl tesserae. The figure of Christ is fIanked by the Virgin and John the Baptist, on a golden ground.

Set into the waIl opposite is the tombstone of Enrico Dandola, Doge of Venice, dated 1205. Further along the gaIlery in an area reserved for imperial portraits we see two mosaies of note. The mosaie to the left is dated to the 1 Ith centuryand shows Christ fIanked by the Empress Zoe and her third husband, the emperor Constantine IX (1042- 1054) . To the right is a 12 century mosaic panel portraying the Virgin and child fIanked by the emperor lohannes Comnenos II (1118- 1143) and the empress Eirene. Their son Alexios is portrayed on a narrow panel on the wall to the right. His pal e and wasted expression is that of a prince who died in his twenties. From this point the apse mosaie of the Virgin man be seen in detail.

Descending from the gallery via the imperial ramp, one may exit from the southern portal of the narthex. The bronze door here is noticable. The door dates from the Hellenistie era and was brought to Istanbul from a templein TaE-, sus. The mosaie over the portal'shows the Virgin, standing, with the Christ child in her arms. To her right the emperor Constantinus Magnus offers up a model of the city, while to her left Justinianus profters a model of the Hagia Sophia.

The gilded tesserae used in the mosaies of the Hagia Sophia were made by spreading gold leaf over alayer of gl ass tesserae, af ter which this was finished with a further layer of glass paste. This prevented the gilding from deteriorating.