St Mawes Castle, Gatehouse, Blockhouse, Magazine And Outer Defences

St Mawes Castle, built between 1540 and 1543 for Henry VIII, is a coastal defence fortification comprising the main keep, gatehouse, blockhouse, magazine and outer defences. The blockhouse dates to the early 16th century, also built for Henry VIII, while the magazine is Victorian.

The castle is constructed of slatestone rubble walls with granite strings, copings, door and window frames. It features a distinctive clover-leaf plan, with a circular keep surrounded by three semi-circular bastions. The walls are exceptionally thick, designed to resist cannon fire. A circular stair turret and lookout tower rises above an embrasure position, topped with a 17th-century lead ogee-shaped roof with finial. The keep and bastions have flat lead roofs, while the gatehouse is slate roofed.

The castle rises three storeys over a kitchen basement. Access is through a polygonal, single-storey gatehouse leading to a two-span bridge with parapets, originally fitted with a drawbridge. The oak door retains its original wicket and hinges. Throughout the building, doorways and other openings feature four-centred arches, with flanking cross slits and chain slits above. A prominent gunport with hoodmould overlooks the gatehouse, surmounted by a coat of arms. The keep is encircled by further similar gunports on the second floor and in the bastions, allowing comprehensive coverage of the surrounding seascape. Battlemented parapets crown the keep and bastions, with provision for mantlets.

The keep's southern entrance is marked by the Royal coat of arms flanked by Tritons bearings on an inscribed scroll. A further inscription runs along the string beneath the keep battlements, interrupted by gargoyles. The second and first floor windows are mullioned with two, four and six lights respectively, some incorporating king mullions, and all protected by the bastion positions. The basement features mullioned windows as well.

The interior retains its original granite newel stair, providing access to all floors with additional stairs serving the bastion parapets. The circular basement kitchen contains a large fireplace with oven, original floor beams (formerly ceiled) set on granite posts, and a niche beside the stair standing on a moulded pedestal. The octagonal ground floor room, originally a mess room, contains two small rooms within the wall thickness—one with a fireplace and keeping place, and another with a further recess possibly a garderobe. The main fireplace features an overmantle with pediment. The octagonal first and entrance floor is half partitioned, creating two flanking chambers with a passage and main hall occupying the remainder. Each room has a fireplace; the principal one includes a niche above, oven to the left and linked keeping place to the right. Original carved oak door heads survive in several locations. A deep shaft with a small chamber at its base lies to the right of the main entrance. The second floor gunroom is octagonal, with deep gunports on each side. Niches beside the gunports in this floor and the bastions may have held powder or shot. Overhead smoke vents, now blocked, indicate the firing arrangements. Wells cut into the moat wall near the bridge and a stone slab in the basement possibly covering another well supplied water to the garrison.

The blockhouse, constructed before the main castle, now stands roofless and features three gunports, a large oven and water cistern. The Victorian-period magazine to the south has a low-pitched masonry roof with granite coping and cornice, and a granite doorcase with low-pitched gable echoing the main roof. Gun emplacements of similar date stand nearby.

The castle saw relatively little military action during its history. It was surrendered in March 1646 by Hannibal Bonython, lieutenant of the castle, to Fairfax, the Parliamentary general, following a brief discussion of terms conducted without a shot being fired.