King John's Castle

King John's Castle is a 13th-century castle located on King's Island in Limerick, Ireland, next to the River Shannon. Although the site dates back to 922 when the Vikings lived on the Island, the castle itself was built on the orders of King John in 1200. One of the best preserved Norman castles in Europe, the walls, towers and fortifications remain today and are visitor attractions. The remains of a Viking settlement were uncovered during archaeological excavations at the site in 1900.
The Viking sea-king, Thormodr Helgason, built the first permanent Viking stronghold on Inis Sibhtonn in 922. He used the base to raid the length of the River Shannon from Lough Derg to Lough Ree, pillaging ecclesiastical settlements. In 937 the Limerick Vikings clashed with those of Dublin on Lough Ree and were defeated. In 943 they were defeated again when the chief of the local Dalcassian clan joined with Ceallachán, king of Munster and the Limerick Vikings were forced to pay tribute to the clans. The power of the Vikings never recovered, and they were reduced to the level of a minor clan, however often playing pivotal parts in the endless power struggles of the next few centuries.

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