During all these centuries, though there were troubles enough from the quarrels of the kings and chiefs, learning and art, as we have seen, were successfully cultivated. But a change came--a woful change--once the Danes began to arrive. These were pirates, all pagans, from Denmark and other countries round the Baltic Sea, brave and daring, but very wicked and cruel, who for a long period kept, not only Ireland, but the whole of western Europe in terror. They appeared for the first time on the coast of Ireland in the year 795, when they plundered St. Columkille's monastery on Lambay Island near Dublin. After this, for more than two hundred years, the country was never free from them, and they plundered and burned and destroyed churches, monasteries, libraries, and homesteads, and killed all that fell in their way, men, women, and children. They were often attacked and routed by the native chiefs; but this did not much discourage them and they generally landed so suddenly, and marched through the country so swiftly, that in most cases they got clear off to their ships, with all their plunder, before the people could overtake them. They settled permanently in various towns on the coast, especially Dublin, Waterford, and Limerick, which they held for a long time. At last they were overthrown by Brian Boru king of Ireland, in a great battle fought at Clontarf near Dublin, on Good Friday, the 23rd April, 1014, of which a full account may be read in the "Child's History of Ireland." After this, though no attempt was made to expel them from the country, they gave little trouble. They became Christians, intermarried with the natives, and settled down to industry and commerce like the rest of the people; and there are many of their descendants to this day in various parts of Ireland. For about a century and a half after the battle of Clontarf, eight Irish kings reigned: but none of them succeeded in mastering the whole country. Some of these were O'Briens of Munster, the descendants of Brian Boru; some O'Loghlins of Ulster, a branch of the O'Neill family, descendants of Niall of the Nine Hostages (see p. 5); and some O'Conors of Connaught. During this period Ireland was greatly disturbed; for the several kings were continually fighting with each other, striving who should be head king: so that the next invaders, when they came, found the country ill prepared to resist them.