Opposite Corfu one can see the mountains of Southern Albania, always difficult to visit, and especially so in the Communist period from 1944 to 1992. This area is called Northern Epirus by the Greeks, and contains many monuments of Greek and Roman civilisation, such as those at Apollonia and Butrint. There are also relics of the Illyrians, claimed by the Albanians to be their ancestors. In the sixth century the Slavs invaded, but the district was recaptured by the Byzantines in the tenth century. There were attacks from the West in the twelfth and thirteenth centuries and a period of anarchy until the Ottoman invasion in the fifteenth.