Frontier wars with varying successes between Scot, Angle, and Dane mark the stormy history of this time. The power of Cnut held back the Scotch attempts upon Nothumberland; but during a lull in the wars the grand-son of the Scottish king married the sister of Earl Siward, and received as her dowry twelve towns in the valley of the Tyne, an astonishingly imprudent arrangement. At the time of the battle of Hastings, the earldom of Northumberland was so far distant from Winchester as to be somewhat out of the control of the King of England; the power of the Scottish kings threatened it; they held twelve towns in Tynedale, and Cumberland was a part of Scotland. The Northumbrians refused to accept William the Conqueror as their king; and had they been able to make good their refusal, they must sooner or later have been conquered by the Scots, and the border-line between England and Scotland would then most probably have been formed by the Tees, the mountain boundary of Westmoreland, and Morecambe Bay. But William was not a king to be played with. He reduced Northumberland to subjection and carried his army into Scotland as far as the river Tay, where he forced the King of Scotland to admit that he, William, was his overlord. Notwithstanding this humiliation, when King William returned to Winchester, the Scots several times went back to their favourite amusement of raiding unhappy Northumberland. One of these invasions took place in the reign of William Rufus (1093), who went north in person. He doubtless recognised the fact that owing to the Scots possessing Cumberland they were in the strong position of being able to attack Northumberland on two sides. He took Cumberland by force of arms, and thus for the first time it became a part of England (the word "Cumberland" means the land of the Cumbrians or Welsh, a Saxon form of the Welsh word Cymry). Rufus rebuilt the strong fortress of Carlisle to defend his new border at its weakest corner. For the most part this border is excellently protected by the natural rampart of the wild Cheviot Hills, and is in every way as good a border as could be devised. It runs in a fairly straight line from south-west to north-east, across a narrow part of the island. But although this border-line proved to be a permanent one, it must not be thought that it remained undisputed. The times were rough, and hardy fighting folk lived on the Border. They had many grounds for quarrel, and took advantage of them all. For one thing, the exact boundary of North Cumberland was never quite defined till 1552; up to which year there was a tract of land between the rivers Esk and Sark, which was claimed by both countries, and therefore called the "Debateable Land." Then the Scots maintained that they were overlords of Northumberland, while the English kings cherished the notion that they were overlords of the whole island of Britain, and the wild spirits on both sides were always ready to fight.