King Charles's Castle

King Charles’s Castle is a ruined artillery fort on Tresco in the Isles of Scilly. It stands on high ground above New Grimsby harbour, built between 1548 and 1551 to guard against French attack. The polygonal granite structure held guns at the front and living quarters at the rear. A 17th-century earthwork was added around it to strengthen its defences. The design was unusual for its time, resembling only Thames blockhouses. Its guns could not fire down into the harbour, making it ineffective. The fort was named after Charles I when Royalists held the islands during the English Civil War. In 1651, Sir Robert Blake’s Parliamentary force bypassed it to capture Tresco. The Royalists destroyed parts of the castle as they retreated. Later, some of its stone was reused to build Cromwell’s Castle nearby. By the 18th century, the site was already described as ruinous. Today, the remains show the gun battery, living rooms and kitchen. The granite walls stand against the wind near the harbour entrance. Visitors walk among the ruins and earthworks, looking down on the water. The site is protected as a scheduled monument and Grade II* listed building. It offers a quiet view of the harbour and the islands beyond.