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Inter-religious conversion

According to early Muslim historians, towns that surrendered without resistance and made treaties with the Muslims were allowed to retain their churches and the towns captured by Muslims had many of their churches converted to mosques. One of the earliest examples of these kinds of conversions was in Damascus, Syria, where in 705 Umayyad caliph Al-Walid I bought the church of St. John from the Christians and had it rebuilt as a mosque in exchange for building a number of new churches for the Christians in Damascus. Overall, Abd al-Malik ibn Marwan (Al-Waleed's father) is said to have transformed 10 churches in Damascus into mosques.

The process of turning churches into mosques were especially intensive in the villages where most of the inhabitants converted to Islam. The Abbasid caliph al-Ma'mun turned many churches into mosques. Ottoman Turks converted nearly all churches, monasteries, and chapels in Constantinople, including the famous Hagia Sophia, into mosques immediately after capturing the city in 1453. In some instances mosques have been established on the places of Jewish or Christian sanctuaries associated with Biblical personalities who were also recognized by Islam.

Mosques have also been converted for use by other religions, notably in southern Spain, following the conquest of the Moors in 1492. The most prominent of them is the Great Mosque of Cordoba, itself constructed on the site of a church demolished during the period of Muslim rule. Outside of the Iberian Peninsula, such instances also occurred in southeastern Europe once regions were no longer under Muslim rule.