In 962 Ildulb mac Causantín, King of Scots, was killed (according to the "Chronicle of the Kings of Alba") fighting the Norse near Cullen, at the Battle of Bauds, and although there is no evidence of permanent Viking settlement on the east coast of Scotland south of the Moray Firth, raids and even invasions certainly occurred. Dunnottar was taken during the reign of Domnall mac Causantín and the "Orkneyinga saga" records an attack on the Isle of May, by Sweyn Asleifsson and Margad Grimsson. The long-ship, the key to their success, was a graceful, long, narrow, light, wooden boat with a shallow draft hull designed for speed. This shallow draft allowed navigation in waters only one metre deep and permitted beach landings, while its light weight enabled it to be carried over portages. Longships were also double-ended, the symmetrical bow and stern allowing the ship to reverse direction quickly without having to turn around. In the "Gàidhealtachd" they were eventually succeeded by the Birlinn, highland galley and lymphad, which, in ascending order of size, and which replaced the steering-board with a stern-rudder from the late twelfth century. Forces of ships were raised through obligations of a ship-levy through the system of ouncelands and pennylands, which have been argued to date back to the muster system of Dál Riata, but were probably introduced by Scandinavian settlers. Later evidence suggests that the supply of ships for war became linked to military feudal obligations. Viking naval power was disrupted by conflicts between the Scandinavian kingdoms, but entered a period of resurgence in the 13th century when Norwegian kings began to build some of the largest ships seen in Northern European waters, until Haakon Haakonson's ill-fated expedition in 1263 left the Scottish crown the most significant power in the region. By the tenth century all of northern Britain was Christianised, except the Scandinavian north and west, which had been lost to the church in the face of Norse settlement. Like every other Christian country, one of the main features of medieval Scottish Christianity was the Cult of Saints. Saints of Irish origin who were particularly revered included various figures called St Faelan and St. Colman, and saints Findbar and Finan. The most important missionary saint was Columba, who emerged as a national figure in the combined Scottish and Pictish kingdom, with a new centre established in the east at Dunkeld by Kenneth I for part of his relics.