With the advent of increasing suppression on Catholicism, the Ottomans initially focused their conversions on the Catholic Albanians of the north in the 17th century and followed suit in the 18th century on the Orthodox Albanians of the south. At this point, the urban centers of central and southern Albania had largely adopted the religion of the growing Muslim Albanian elite. Many mosques and tekkes were constructed throughout those urban centers and cities such as Berat, Gjirokastër, Korçë and Shkodër started to flourish. In the far north, the spread of Islam was slower due to Catholic Albanian resistance and the inaccessible and rather remote mountainous terrain.