the same time, Muirchertach was also under threat from Magnus Barefoot of Norway, who had returned with a larger force than his first Irish Sea campaign, possibly with the intention of invading Ireland. Magnus had earlier raided Inis Cathaigh (Scattery Island) at the Shannon estuary in 1101, possibly testing the situation and defenses of Ireland. Magnus agreed to provide military support for the High King in his war against the men of Ulster. They forged an alliance, cemented by the marriage of Muirchertach's daughter, Bjaðmunjo, to Magnus's son, Sigurd. The treaty also saved Ireland from Norse raids, but the Irish lost most of their control in the Isles to the Norwegians. Muirchertach also recognised Norwegian control over Dublin and Fingal, with the western lands of the Kingdom of Norway under the control of Sigurd, who was announced as co-king alongside Magnus on the day of his wedding. Muirchertach and Magnus campaigned together in Ulster throughout late 1102 and early the next year. Contrary to the Norse sagas, the Irish Annals describe the campaigns as largely unsuccessful. Norse sources say Magnus spent the winter in the High King's palace at Kincora in Killaloe with Muirchertach, but it is also possible that he wintered in Dublin. In the summer of 1103, Muirchertach launched an offensive against Domnall Ua Lochlainn, but was defeated on 5 August at the Battle of Mag Coba. After this, with enemies to the north and Magnus threatening his throne, it is possible Muirchertach wanted Magnus out of the way. There is confusion surrounding the death of Magnus. Norwegian sources say Muirchertach was supposed to bring Magnus provisions for his return to Norway. When Muirchertach did not show up at the agreed time, Magnus became suspicious the Irish were going to attack. On 24 August 1103, St. Bartholomew's Day—or the day before, according to one source—Magnus gathered his army and landed on the coast of northeastern Ireland. It is possible he made an incautious cattle raid, and the Ulaid mistook the Norwegians for cattle-raiding Hebrideans. Alternatively, it is possible that Muirchertach ordered the Ulaid to bring Magnus supplies, but the Ulaid took this is an order to ambush him. It is also possible that powerful men in Norway wanted Magnus removed from the throne, and bribed a contingent of his forces to desert back to their ships during the battle. As Magnus landed on the shore, a large Irish