r driving
them away, with the aid of his fellow chieftains.

Thus for a time Ireland was freed. It was conquered again by Olaf the
White, who in 852 defeated some Danes who had taken Dublin, and then,
like Thorgisl, began to build castles and tax the people. Two other
viking leaders won kingdoms in Ireland, but Olaf was the most powerful of
them all, and the kingdom founded by him lasted for three hundred and
fifty years. From Dublin Olaf sailed to Scotland and England, the booty
he won filling two hundred ships.

The sea-rovers did not confine their voyages to settled lands. Bold ocean
wanderers, fearless of man on shore and tempest on the waves, they
visited all the islands of the north and dared the perils of the unknown
sea. They rounded the North Cape and made their way into the White Sea as
early as 750. The Faroe, the Orkney and the Shetland Islands were often
visited by them after 825, and in 874 they discovered Iceland, which had
been reached and settled by Irishmen or Scots about 800. The Norsemen
found here only some Irish hermits and monks, and these, disturbed in
their peaceful retreat by the turbulent newcomers, made their way back to
Ireland and left the Norsemen lords of the land. From Iceland the rovers
reached Greenland, which was settled in 986, and about the year 1000 they
discovered North America, at a place they named Vinland.

Such is, briefly told, the story of the early Norse wanderers. They had a
later tale, of which we have told part in their conquest of Ireland.
Though at first they came with a few ships, and were content to attack a
town or a monastery, they soon grew more daring and their forces larger.
A number of them would now fortify themselves on some coast elevation and
make it a centre for plundering raids into the surrounding country. At a
later date many of them ceased to pose as pirates and took the role of
invaders and conquerors, storming and taking cities and founding
governments in the invaded land.

Such was the work of Thorgisl and Olaf in Ireland and of Rollo in
Normandy. England was a frequent field of invasion after 833, which
continued until 851, when King Ethelwulf defeated them with great
slaughter. Fifteen years later they came again, these new invaders being
almost all Danes. During all his reign Alfred the Great fought with them,
but in spite of his efforts they gained a footing in the island, becoming
its masters in the north and east. A century later, in 1016,