 Polruan also has a blockhouse fortification built in the 14th century that guards the entrance to the river Fowey, one of a pair—its partner being situated on the Fowey side of the river.The Polruan blockhouse is well preserved due to the efforts of various enthusiastic councillors and conservationists on the Polruan side of the river, in contrast to the blockhouse in Fowey.Between the two blockhouses was strung a defensive chain to prevent enemy ships entering the harbour, the chain being lowered for friendly vessels.