In Ireland the power of the Scandinavians was shown in the foundation of two kingdoms, along the two main lines of sea traffic--Dublin on the eastern sea, and Limerick on the Atlantic. The Norwegian kingdom on the Liffey had its centre in the mound raised by the river-side for its Thing or Moot, near where the Dublin Parliament House rose nine hundred years later. The kingdom stretched over a narrow strip of shore, the memory of which was preserved for a thousand years, till a generation ago, in the jurisdiction of the Dublin Corporation over a long line of coast from the river Delvin below Drogheda to Arklow. Four fiords--Strangford and Carlingford to the north, and Wexford and Waterford to the south--lay outside the actual kingdom of Dublin, but were closely connected with it. Waterford kings were at times of the same family as the Dublin kings, and in the ninth and tenth centuries Waterford was sometimes independent and sometimes united to Dublin. Dublin commanded a double line of commerce--from Scandinavia to Gaul, and by York to Novgorod and the Eastway. The kingdom was in close connection with the Danish kingdom of Northumbria, with its capital at York. For Danish Northumbria, opening on the North Sea by the Humber, formed the common meeting ground, the link which united the Northmen of Scandinavia and the Northmen of Ireland. A mighty confederation grew up. Members of the same house were kings in Dublin, in Man, and in York. Their descendants were among the chief settlers in Iceland. The Dublin kings married into the chief houses of Ireland, Scotland, and the Hebrides. The sea was the common highway which bound the powers together, and the sea was held by fleets of swift long-ships with from ninety to a hundred and fifty rowers or fighting men on board. The Irish Channel swarmed with ships of the Dublin kingdom. It became the mart of the Scandinavian traders, of Icelandic sailors, and men of Norway, and merchant princes landing from their cruise to sell their merchandise or their plunder. “You must this summer make a trading voyage,” said Earl Hakon to his friend Thori Clack, “as is customary now with many, and go to Dublin in Ireland.” Far-travelled traders carried from Dublin and York, deep into the inland of Russia, English coins and weapons and ornaments such as were used in Great Britain and Ireland.