The tenth and eleventh centuries produced a school of Irish historians whose chief work was to reduce the old miscellaneous matter of tradition to unity and sequence. It would have been well if they had been satisfied with so much, but they went farther. In dealing with the pre-Christian period, they tampered with tradition in two ways. Where they found definite elements of heathenism, they either cut these out or furbished them in a guise which they considered consonant with Christian belief; and this can be shown to have been done consciously and deliberately. They also took a free hand in devising a system of chronology for events that had no chronology. On this point, they did not all act together, and so, for such epochs as the Gaelic invasion, we have six or seven different dates varying from the fourth to the eighteenth century B.C. Not withstanding these defects in their work, the historians of this period acquired in later times a degree of authority that stood up as a barrier in front of the past. Their highly artificial treatment was vested with all the sanctity of veritable tradition. The main work that has now to be done by students of Irish antiquity is to get behind this barrier and bring into the light the abundant remains of older tradition that are extant. I have said that, in the minds of the scattered Norse community, the battle of Clontarf broke the victorious prestige of their race. It happened at a critical moment, for in the year before it, in 1013, the Danish conquest of England had been completed, and all England had submitted to the rule of Sveinn, king of Denmark. Nearly a century later, king Magnus of Norway endeavoured to restore the empire of the Norsemen. He succeeded in bringing under his authority all the Scottish islands, Caithness, part of Argyle, and the Isle of Man. Once more, Ireland shaped the course of history. In 1102, Magnus, then in the Isle of Man, sent an embassy to Ireland threatening war, and no doubt demanding tribute. Muirchertach O'Briain, then king of Ireland, obtained a year's truce. About the same time, Muirchertach made peace for a year with Domhnall MacLochlainn, king of Tyrone, who opposed his claim to the high-kingship. Next year, 1103, Muirchertach marched against Domhnall, but was defeated in the neighbourhood of Banbridge. About the same time, and probably taking advantage of this internal conflict, Magnus made a landing on the Ulster coast, but was cut off and fell in the fight. With his fall, the prospect of a Norse empire came to an end.