Cromwell's Castle

Standing on a rocky promontory guarding the lovely anchorage between Bryher and Tresco, this round tower is one of the few surviving Cromwellian fortifications in Britain, built after the conquest of the Royalist Scillies in 1651.

This tall round tower, standing on a low projecting shelf of rock, is one of only a few stone fortifications that survive from the Interregnum (1649–60) and takes its name from Oliver Cromwell, Lord Protector of England.

The fort replaced a Tudor blockhouse on the site, and superseded King Charles’ Castle, which had been built in the 1550s on higher ground but proved to be poorly sited and was partly demolished to provide building stone for this later castle.

Royalists had held out on the Isles of Scilly for most of the Civil War period. Increasing tension with the Dutch, and in particular the arrival of a Dutch fleet off the islands in March 1651 demanding reparations from the Royalist privateers based there, prompted Parliament to send Robert Blake, the most successful admiral of the 17th century, to recapture these strategic islands.

The castle was built in 1651, following swiftly on Blake’s success, to guard one of the main routes of entry to the heart of the islands and the deep water approach to New Grimsby harbour. It faced a potential enemy with an impossible choice.

No fleet could hope to land troops on this side of Tresco unless it had first destroyed or captured the castle, but the chances of destroying the castle by gunfire from the sea were very slim. The fort was considered worth updating a century later, when a platform for cannon was added on the seaward side.