Cromwell's Castle

Visitor Guide

Cromwell's Castle is reached on foot from New Grimsby, Tresco's main settlement on this side of the island, following a coastal path north along a heather-covered hillside to the tower's dramatic shoreline setting. There is no vehicle access anywhere on Tresco for visitors, so the walk itself, with views out across the anchorage to Bryher, is very much part of the experience.

Inside, a steep spiral stone staircase climbs through the tower's two upper storeys to the roof gun platform, where the six original gunports still frame views out across New Grimsby Sound. The later 18th-century gun platform on the seaward side is worth a look too, a reminder that this small tower remained a working part of Scilly's coastal defences long after Cromwell's soldiers had gone. Combined with King Charles's Castle on the hill directly above, visitors can trace more than a century of changing military architecture within a single short walk.

Allow around thirty to forty-five minutes to explore Cromwell's Castle itself, considerably longer if combining it with King Charles's Castle and the Old Blockhouse further along the coast, a popular circular walk taking in all three of Tresco's principal fortifications. A shop south of New Grimsby harbour offers refreshments, while Tresco Abbey Garden, a little further south on the island, makes for a very different but equally rewarding stop on the same day.

History

Cromwell's Castle takes its name from the period of its construction rather than any direct connection to Oliver Cromwell himself, having been built in 1651 in the immediate aftermath of the parliamentary reconquest of the Isles of Scilly during the English Civil War. The islands had remained a stubborn Royalist stronghold even after the king's cause was lost on the mainland, and it took a determined naval campaign under Admiral Robert Blake to bring them back under parliamentary control, a victory secured only months before the castle's construction began.

The urgency behind the new fort's construction is captured by events that same spring: in March 1651, a Dutch fleet appeared off the islands demanding reparations from Royalist privateers who had been operating from Scilly's harbours, a stark reminder that even after the Civil War's end the islands remained exposed to continental naval power. Blake's garrison needed a fortification capable of properly defending New Grimsby, recognised as one of the safest and most strategically important anchorages in the archipelago, guarding as it did one of the main routes of entry to the heart of the islands.

The tower's design reflects this defensive priority above all else. A circular structure with a basement, two upper floors and a rooftop gun platform, its walls almost 13 feet thick at their base, it was built to withstand sustained bombardment while presenting the smallest possible target from the sea. An internal spiral staircase connects the floors, while six widely splayed gunports around the roof gave the garrison a genuinely all-round field of fire over the surrounding anchorage, ensuring no attacking vessel could approach unchallenged.

The castle's strategic value endured well beyond the Interregnum that gave it its name. During the 18th century, as renewed fears of French and Spanish naval power returned to English coastal defence planning, an additional gun platform was constructed on the seaward side of the tower, designed to mount six further cannon and reflecting Cromwell's Castle's continued importance a full century after its original construction.

Unlike the earlier King Charles's Castle on the hillside above, whose guns famously could not depress far enough to threaten shipping approaching at sea level, Cromwell's Castle was deliberately sited low, right on the shoreline, correcting exactly the flaw that had made its predecessor militarily useless. Its builders clearly learned from a century of Tresco's fortification mistakes, and the result was a genuinely effective coastal defence that remained in credible military use far longer than the fort it replaced.

Today the tower is owned and managed by English Heritage, one of the very few surviving stone fortifications from the Cromwellian Interregnum anywhere in Britain, and remains freely open to visitors exploring Tresco's dense cluster of historic coastal defences.

Important Features

• The gun tower: a circular Cromwellian structure with walls nearly 13 feet thick, built in 1651.
• The rooftop platform: six widely splayed gunports giving an all-round field of fire over New Grimsby Sound.
• The internal staircase: a spiral stone stair connecting the tower's basement and two upper storeys.
• The 18th-century gun platform: a later seaward addition built to mount six further cannon.
• Its shoreline setting: positioned directly on the rocks to command the deep-water channel into the islands.
• Proximity to King Charles's Castle: the earlier, ruined Tudor fort on the hillside directly above.

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 Cromwell's Castle before you travel.

Visit the official English Heritage website