 The arrival of the Muslim Arabs brought drastic changes to Gaza ; its churches were transformed into mosques , including the Cathedral of John the Baptist ( previously the Temple of Marnas ) which became the Great Mosque of Gaza . Gaza 's population adopted Islam as their religion relatively quick in contrast with the city 's countryside . Eventually , Arabic became the official language . The Christian population was reduced to an insignificant minority and the Samaritan residents deposited their property with their high priest and fled the city east upon the Muslim conquest . Gaza was placed under the administration of Jund Filastin ( " District of Palestine " ) of Bilad al @-@ Sham province during Rashidun rule , and continued to be a part of the district under the successive caliphates of the Umayyads and Abbasids . 
