The French Navy attacked the port of Fowey in 1457, and prompted the building of two defensive blockhouses on each side of the estuary. One of them, Polruan Castle, is now one of the Fowey valley’s most attractive historic sites. The Castle was equipped with artillery in Tudor times, but its most effective military weapon was not a gun – but a chain. The chain ran across the bed of the river to the companion castle on the Fowey side. When potential enemies were sighted, it was simply raised through the water, providing an impenetrable barrier to the settlements behind.