The settlement of Rhuddlan is likely to have owed its origin to the presence at this point, from very early times, of the lowest fording-place on the river, from which a track led across the marsh to Vaynol and beyond.
At the command, William the Conqueror, a new castle of the motte-and-bailey pattern, which marked every stage of the Norman penetration, was thrown up at Rhuddlan in 1073 by Robert of Rhuddlan, a kinsman and lieutenant of Hugh d'Avaranches, earl of Chester.
Rhuddlan was in Royalist hands during the Civil War, until forced to capitulate in 1646.