In 835 the attacks on England were renewed after an interval of 40 years, but as they now stand in close connexion with contemporary invasions of Frankish territory there is every reason to believe that they were of Danish rather than of Norse origin. The attacks began in the south and west but they soon spread to East Anglia and Lindsey. In 842 the same army ravaged London, Étaples and Rochester. In 851 Aethelstan of Kent defeated the Danes at sea in one of the rare battles fought with them on their own element, and in the same year they remained for the winter in Thanet, probably owing to the loss of their ships. The size and importance of these attacks may be gauged from the fact that in this year a fleet of some 350 Danish ships sailed up the Thames. It was probably that same fleet, with slightly diminished numbers, which in 852 ravaged Frisia and then sailed round the British Isles, came to Ireland, and captured Dublin. In 855 the Danes wintered for the first time in Sheppey and we reach the same point in the development of their attacks on England to which they had already attained in Ireland. We pass away from the period of raiding. The Danes now came prepared to stay for several years at a time and to carry on their attacks with unceasing persistency. The course of events in the Frankish empire ran on much the same lines as in England and Ireland during these years except that here trouble arose on the land boundary between Denmark and the Franks as well as on the sea-coast. Alarmed by the conquest of the Saxons the Danish king Guðröðr collected a fleet at Slesvík and in 808 he crossed the Eider and attacked the Abodriti (in Mecklenburg-Schwerin), a Slavonic tribe in alliance with the Franks. He also sent a fleet of some 200 vessels to ravage the coast of Frisia, laid claim to that district and to Saxony, north of the Elbe, and threatened to attack Charlemagne in his own capital. The emperor was preparing to resist him when news arrived (810) of the death of Guðröðr at the hands of one of his followers and the consequent dispersal of the Danish fleet.