The castle is built on the foundations (or the podium) of the earlier Roman temple of Claudius (built between AD 54–60).[5] These foundations, with their massive vaults, have since been uncovered and can be viewed today on a castle tour.

The castle was ordered by William the Conqueror and designed by Gundulf, Bishop of Rochester. Building began between 1069 and 1076 under the supervision of Eudo Dapifer
From Wikipedia
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