Many Slav tribes, seeking refuge from the domination of the Avars, crossed the Danube in their light canoes, and established themselves in the wooded slopes of the Balkans, or the marshes of the Dobrudscha, where they found the cover that they loved. The Moesian provincials had been so thinned by two hundred years of raiding suffered at the hands of Goth, Hun, and Avar, that the Slavs found the land almost wholly uninhabited. Outside the great Danube fortresses, and the large towns like Naissus or Sardica, the population had almost entirely disappeared. [Sidenote: The Slavs cross the Danube.] Avoiding battles with the garrisons of the towns, the Slavs slipped between them, and spread over the face of the deserted land, pitching their rude huts in the most secluded spots that they could find. They were not only intruders, but enemies, for they were keenly set on plunder, waylaid every party of travellers that strove to pass from town to town, and laid ambuscades for every body of soldiers that was not too numerous for them to cope with. From 585 to the very end of his reign Maurice was engaged in a desperate struggle against Slav and Avar, which raged over the whole of the Balkan peninsula. The invaders gradually pressed southwards, though they suffered many defeats, and though whole tribes of Slavs were sometimes exterminated. The enemy, though individually contemptible, seemed to draw on endless reserves of strength, as horde after horde slipped across the Danube, and threw itself into the glens of the Balkans. The effect of these invasions is well described by a contemporary chronicler, John of Ephesus: ‘The first years of Maurice were famous for the invasion of the accursed people called Slavonians, who overran Greece and all the lands about Thessalonica and Thrace, plundering many towns, and devastating and burning, and reducing the people to slavery. They have made themselves masters of the whole country, and settled in it by main force, and dwell in it as though it were their own. Four years have now passed, and still they live at their ease in the land, and spread themselves abroad, as far as God permits them, and ravage and burn and take captive, and still they encamp and dwell there.’