Scarcely was Sweyn invested with the dignity, when he found an enemy as powerful as Magnus, and less generous, in Harald Hardrade, who claimed the Danish crown. The assertion of this claim led to many years of warfare, ruinous to both kingdoms, but especially to Denmark, the coasts of which were often ravaged. In general the advantage rested with the Norwegian monarch, who, in 1064, obtained a great victory over the Danish fleet at the mouth of the Nissa. With great difficulty Sweyn escaped into Zealand, and began to collect a new armament. Fortunately the mind of Harald was now disposed to peace. Sixteen years of hostilities had brought him little advantage; the fortune of war was dubious; and the Danes, like their king, were averse from a foreign yoke. The two monarchs met, and entered into a treaty, which left affairs just as they had been at the death of Magnus. These were not the only hostilities in which they were engaged. Both undertook predatory expeditions to the English coast; but they could obtain no advantage over the vigilant and intrepid monarch (William I.), who now swayed the sceptre of that kingdom.[145] Sweyn too had the mortification to see his own coasts ravaged (those of Holstein) by the Vandalic pirates, who had renounced Christianity, and who laid both Sleswic and Hamburg in ashes. Before he could reach them they retired. Subsequently he was persuaded to march against the Saxons, then at war with the emperor; but his troops having no inclination to exasperate a people with whom they had long been on terms of amity, he desisted from the undertaking. [Sidenote: 1066 to 1070.]