evidence: The Danes clearly had the Norse – and not the Irish – as their target; in 851 CE they attacked both Viking Dublin and the longphort at Linn Duachaill, and defeated the Norse after a three-day long naval battle at Carlingford Lough in 853 CE, after which the Norse bounced back and finally drove the Danes off. With the Norse and the Danish as rival Viking groups, according to Dáibhí Ó Cróinín (250-251), it is not impossible that the Irish had initiated an alliance with the Danes and then sat back to watch things unfold.