The building lies in Istanbul, in the district of Beyoğlu, in the neighborhood of Karaköy (ancient Galata), on Galata Mahkemesi Sokak, not far from the northern shores of the Golden Horn. It is surrounded by artisan shops.

Byzantine period

During the sixth century a Byzantine church, possibly dedicated to Saint Irene, was built here. Of this building, only part of a wall survives today. The tradition which affirms that a mosque was built on this place during the Arab Siege of 717-18 by Maslama ibn Abdal Malik (a commander and cousin of Caliph Umar ibn AbdulAziz) must be considered a legend.

In 1233, during the Latin domination after the Fourth Crusade, this church was replaced with a new one, dedicated to Saint Paul (San Paolo) and given to the Dominicans. The building must have been opened to the cult shortly before 1260, a date which is found on a tombstone found in the church.

In 1299, the Dominican Friar Guillaume Bernard de Sévérac bought a house near the church, where he established a monastery with 12 friars. In 1307, Byzantine Emperor Andronikos II Palaiologos moved the Dominicans of Constantinople to the Genoese-held suburb of Pera.

The church of San Paolo was rebuilt in 1325. From this time on the church was officially dedicated to San Domenico, but local voyagers continued to use the ancient denomination.  In 1407 Pope Gregory XII, in order to ensure the maintenance of the church, conceded indulgences to the visitors of the monastery of San Paolo.

After the Fall of Constantinople, according to the Capitulations of the Ottoman Empire with the Republic of Genoa, the church, which by that time was known by the Turks under the name of Mesa Domenico, remained in Genoese hands, but between 1475 and 1478 it was transformed, with minor modifications, into a mosque by the Ottoman Sultan Mehmed II and became known as Galata Camii ("Galata Mosque") or Camikebir ("Great Mosque"). The friars were transferred in the friary of San Pietro in Galata in 1476, while all the altar clothes had already been brought to Genoa, and the archives to Caffa.

Towards the end of the century Sultan Bayezid II assigned the building to the Muslims of Spain (Andalusia), who fled the Spanish Inquisition and migrated to Istanbul; hence the present name Arap Camii (Arab Mosque).  Sultan Mehmet III repaired the building, and towards the end of seventeenth century the houses which encroached upon the mosque were pulled down in order to avoid noise.

After the 1731 Great Fire of Galata, in 1734/35 the mother of Mahmut I, Saliha Sultan renovated the building, changing the windows and the portal from the Gothic to the Ottoman style.[8] After another fire in 1808, in the mid-nineteenth century, the daughter of Mahmud II, Adile Sultan, repaired the mosque again and in 1868 built a şadirvan (fountain for ritual ablutions before praying) in the courtyard.[

Between 1913 and 1919, Giridli Hasan Bey extensively restored the church again. During the replacement of the wooden floor, several Genoese tombstones dating back to between the first half of fourteenth and up to the middle of the fifteenth centuries were discovered. They were brought to the Istanbul Archaeology Museum.

Source : http://en.wikipedia.org/wiki/Arap_Mosque