Ancient architecture is found throughout Albania and most visible in Byllis, Amantia, Phoenice, Apollonia, Butrint, Antigonia, Shkodër and Durrës. Considering the long period of rule of the Byzantine Empire, they introduced castles, citadels, churches and monasteries with spectacular wealth of visible murals and frescos. Perhaps the best known examples can be found in the southern Albanian cities and surroundings of Korçë, Berat, Voskopojë and Gjirokastër. Involving the introduction of Ottoman architecture there was a development of mosques and other Islamic buildings, particularly seen in Berat and Gjirokastër.