On the North-East the Frankish border, after 785, was fringed by Slavonic tribes, all ancient enemies of the Saxon. [Sidenote: Conquest of the Northern Slavs.] These were the Abotrites in the north—in the modern Mecklemburg—the Wiltzes beyond them in western Pomerania, and the Sorbes in Brandenburg, on the Havel and Spree. These tribes, like their kindred whom we have already met in the Balkan peninsula, were rude peoples, and not very formidable enemies, owing to their subdivisions under petty princes, and their incapacity for union. Though numerous and not unwarlike, all the Slavs between Elbe and Oder were subdued by Charles in a single campaign. He crossed the Elbe in 789 with an Austrasian army, strengthened by levies of Frisians and of Saxons, who served gladly against their ancestral foes. The terror of his name seems to have stricken the Slavs with dismay. After a very slight resistance, first the Abotrites and their chief king Witzin, then the Wiltzes and their chief king Dragovit did homage to Charles, gave him as many hostages as he chose to demand, and consented to pay him a tribute and to receive the Christian missionaries whom he prepared to send among them. The Frankish army marched through moors and woods till it saw the Baltic at the mouth of the Peene in Pomerania, and then returned with some booty and no loss to the banks of the Rhine. So thoroughly were the Slavs subdued that during the next revolt of the Saxons they did not take the opportunity of disowning their homage to Charles, but came to help him against the rebels (795). Witzin, prince of the Abotrites, was actually slain by the Eastphalians while in arms for the Franks, and his death was well revenged by the king, who harried the lands along the Elbe with exceptional severity to atone for his ally’s slaughter. In a later Saxon rising (798) we again find the Abotrites taking arms at the bidding of Charles. Their new king Thrasuco reconquered the Nordalbingians without Frankish aid, and brought their chiefs in bonds to the king’s feet, ‘whereupon Charles honoured him marvellously, and gave the Slavs great gifts.’ [Sidenote: Wars of Dane and Slav.] Ten years later the same prince and people fought valiantly against the Danes when they invaded the northern frontier of Charles’s realm, though their neighbours the Wiltzes on this occasion deserted to the enemy. The latter people, however, were subdued again in 812, at the very end of the great king’s reign, so that he left his eastern boundary undiminished at his death. On the whole the Slavs of the North were not by any means the most difficult to rule of the many races with whom Charles had to deal.