Two entries with the name Castle of the Horn.

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Castle of the Horn

Castel del Cor

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The fortress ruled by the Lord of the Horn in the Land of the Horn.

The name of the castle reflected a horn hanging outside which, when blown, summond the Lord to fight. Perceval blew the horn and defeated the Lord in combat.

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Source
Second Continuation of Chrétien’s Perceval | Attributed to Wauchier of Denain, c. 1200

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Castle of the Horn

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A castle in Gaul captured by Arthur during his war with Claudas. Arthur gave it to Bors who, in turn, bestowed it on the (unnamed) husband of the Lady of the Lake.

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Source
Vulgate Lancelot | 1215-1230

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