Conversion of non-Islamic places of worship into mosques

The conversion of non-Islamic places of worship into mosques occurred during the life of Muhammad and continued during subsequent Islamic conquests and invasions and under historical Muslim rule. Hindu temples, Jain Temples, churches, synagogues, and Zoroastrian fire temples have been converted into mosques.
Several such mosques in the areas of former Muslim rule have since been reconverted or have become museums, including the Parthenon in Greece and numerous mosques in Spain, such as Mosque–Cathedral of Córdoba. Conversion of non-Islamic buildings into mosques influenced distinctive regional styles of Islamic architecture.
Upon the capture of Jerusalem, it is commonly reported that Umar refused to pray in the Church of the Holy Sepulchre in spite of a treaty. The architecturally similar Dome of the Rock was built on the Temple Mount, which was a destroyed site of the holiest Jewish temple, destroyed by the Romans in AD 70 and with consistent Jewish presence in Jerusalem has always been a site of religious prayer for Jews. Umar initially built there a small prayer house which laid the foundation for the later construction of the Al-Aqsa Mosque by the Umayyads.
The Fethija Mosque (since 1592) of Bihać was a Catholic church devoted to Saint Anthony of Padua (1266).
Following the Ottoman conquest of Cyprus, a number of churches (especially the Catholic ones) were converted into mosques. A relatively significant surge in church-to-mosque conversion followed the 1974 Turkish Invasion of Cyprus. Many of the Orthodox churches in Northern Cyprus have been converted, and many are still in the process of becoming mosques.
Numerous orthodox churches were converted to mosques during the Ottoman period in Greece. After the Greek War of Independence, many of them were later reconverted into churches. Among them:
Following the Ottoman conquest of the Kingdom of Hungary, a number of churches were converted into mosques. Those that survived the era of Ottoman rule, were later reconverted into churches after the Great Turkish War.
A Catholic church dedicated to Saint Vincent of Lérins, was built by the Visigoths in Córdoba; during the reign of Abd al-Rahman I, it was converted into a mosque. In the time of the Reconquista, Christian rule was reestablished and the building became a church once again, the Cathedral of Our Lady of the Assumption.
After the Ottomans conquered Mangup, the capital of Principality of Theodoro, a prayer for the Sultan recited in one of the churches which converted into a mosque, and according to Turkish authors "the house of the infidel became the house of Islam."
The Islamic State converted a number of churches into mosques after they occupied Mosul in 2014. The churches were restored to their original function after Mosul was liberated in 2017.
The Herodian shrine of the Cave of the Patriarchs in Hebron, the second most holy site in Judaism, was converted into a church during the Crusades before being turned into a mosque in 1266 and henceforth banned to Jews and Christians. Part of it was restored as a synagogue by Israel after 1967. Other sites in Hebron have undergone Islamification. The Tomb of Jesse and Ruth became the Church of the Forty Martyrs, which then became the Tomb of Isai and later Deir Al Arba'een.
Following the Ottoman conquest of Anatolia, virtually all of the churches of Istanbul were converted into mosques except the Church of Saint Mary of the Mongols.
Elsewhere in Turkey numerous churches were converted into mosques, including:
Hundreds of Armenian Churches were converted into Mosques in Turkey and Azerbaijan.
The conversion of non-Islamic religious buildings into mosques during the first centuries of Islam played a major role in the development of Islamic architectural styles. Distinct regional styles of mosque design, which have come to be known by such names as Arab, Persian, Andalusian, and others, commonly reflected the external and internal stylistic elements of churches and other temples characteristic for that region.