Grosnez Castle, Medieval castle ruins in Saint Ouen, Jersey.
Grosnez Castle is a granite fortress ruin perched on a clifftop, featuring granite walls about 16 feet high on the landward side. The site includes a gatehouse with arrow slits and defensive bastions that command views over the coastal landscape.
Construction began in 1330 under Sir John des Roches during the Hundred Years War to protect the island's farmers from French attacks. In 1483, stones from the castle were repurposed to strengthen the nearby Saint Ouen's Manor.
The name Grosnez comes from Norse words meaning grey headland, reflecting how Scandinavian language shaped place names across the Channel Islands. Visitors today can see this Nordic heritage echoed in many location names throughout Jersey.
Access to the ruins is maintained year-round by Jersey Heritage and available to visitors. From the site you can see clear views toward Alderney and other Channel Islands, as well as the surrounding seascapes.
The castle appears on Jersey's 50 pence coin, making it an image stamped into the island's official currency. This recognition reflects its standing as one of Jersey's defining historical landmarks.
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