King Charles's Castle

Visitor Guide

King Charles's Castle is reached via a steep footpath climbing across heather-studded hillside from New Grimsby, Tresco's main harbour settlement on this side of the island. There is no vehicle access anywhere on Tresco, so the walk up is unavoidable, and sturdy, grippy footwear is well worth having for the climb.

Once at the top, the castle's hilltop position immediately explains its own downfall: the strait and harbour it was meant to defend lie so far below that it becomes obvious why 16th-century gunners struggled to bring their weapons to bear on shipping passing beneath. The ruins themselves, angular walls in the older Henrician gun-fort style, are modest but atmospheric, and the views from this high vantage point across New Grimsby Sound to Bryher are genuinely spectacular, arguably the site's greatest asset today even if they were of limited use to its original garrison.

Allow around twenty to thirty minutes to explore the ruins, though most visitors combine King Charles's Castle with the walk down to Cromwell's Castle directly below on the shoreline, an easy and popular circular route that neatly illustrates the contrast between the two forts' very different fortunes. A shop near New Grimsby harbour offers refreshments, while Tresco Abbey Garden a little further south makes for a very different addition to the same day.

History

King Charles's Castle was built during the reign of Edward VI, between 1547 and 1553, as part of the ongoing mid-Tudor effort to strengthen England's coastal defences against the continuing threat of invasion from France or Spain. Its purpose was to protect the narrow strait leading past New Grimsby harbour towards St Mary's, an anchorage of real strategic importance to control of the wider archipelago, and its construction followed the angular gun-fort style already familiar from fortifications built under Edward's father, Henry VIII.

Even by the standards of its own period, the design looked somewhat dated. At the very same time, engineers working on St Mary's were building the far more modern, arrow-headed bastions of Harry's Walls, a design first developed in Italy in the late 15th century and considerably more sophisticated than the older-style fortification chosen for Tresco. This contrast between the two contemporary forts illustrates just how rapidly military architecture was evolving during the mid-16th century, and how quickly a fort's design could become outdated even before construction was finished.

King Charles's Castle's most serious problem, however, was not its style but its siting. Built approximately 40 metres above sea level on a crest overlooking the strait, the fort's guns had to be aimed at such a steep downward angle to threaten passing ships that, in practical terms, cannonballs would have rolled straight out of the barrels before they could be fired. This fundamental flaw rendered the castle largely ineffective as a genuine coastal defence almost from the moment it was completed, a fact that became increasingly clear as the 16th century wore on. By the 1590s, the islands' defensive priorities had shifted decisively to St Mary's, where the much better-positioned Star Castle was built on the headland later known as The Garrison, leaving King Charles's Castle militarily sidelined.

The castle nonetheless played a role in the English Civil War. Royalist forces, who held the Isles of Scilly for much of the conflict, garrisoned it regardless of its limitations, but when Parliamentarian troops under Admiral Robert Blake moved to retake the islands in 1651, they simply bypassed King Charles's Castle entirely, landing elsewhere on Tresco rather than confronting a fort whose weaknesses were by then well understood. In the aftermath, the castle was partly demolished, its stone repurposed to build Cromwell's Castle on the shoreline directly below, a far more effective fortification that corrected precisely the low-siting flaw that had doomed its predecessor. Today the ruins of King Charles's Castle are cared for by English Heritage, a well-preserved and genuinely instructive example of Tudor military engineering undone by its own hilltop ambition.

Important Features

• The angular gun-fort walls: surviving ruins in the older Henrician fortification style of the 1540s.
• Its hilltop position: sited around 40 metres above the strait, the fatal flaw in the fort's design.
• Views over New Grimsby Sound: the site's genuine highlight today, sweeping outlooks across to Bryher.
• Evidence of stone robbing: sections removed to build the more effective Cromwell's Castle below.
• Its Civil War garrison: held by Royalists but bypassed by Parliamentarian forces in 1651.
• Proximity to Cromwell's Castle: the corrective fortification built directly below on the shoreline.

Visitor Information

Things to Do Nearby

Frequently Asked Questions

Official English Heritage Site

For the latest access information, events and any temporary restrictions, check the official English Heritage page for King Charles's Castle before you travel.

Visit the official English Heritage website