stands on guard, protecting Tenby’s Castle beach from . . . well, these days, not much more than easterly winds attacking the Pembrokeshire coastline. But in the past, this small outcrop of limestone, a mere 200 meters long, by 60 metres wide, and 25 metres high, has had ten different lives, including defending the nation.

Life 1: Isolated chapel

Cut off from the UK mainland twice a day at high tide, St Catherine’s acquired its name and its first life, from a small chapel built here by Christians seeking solitude and peace to be closer to God. St Catherine is the patron saint of young girls, students, philosophers, and craftspeople working with wheels, such as spinners and weavers. The woolen industry, in particular weaving and spinning, grew considerably during the 12th century when Cistercian Monks established monasteries in Wales. (Caldey Island, with its Cistercian Monastery, is visible from Tenby and St Catherine’s Island.)

Life 2: Palmerston fort

In 1859, Lord Palmerston’s Royal Commission on the Defence of the United Kingdom recommended building a fort here to protect the naval dockyard at nearby Pembroke, as well as protect the deep anchorage of Milford Haven. (Milford Haven is the deepest estuary in Wales, and one of the deepest found anywhere in the world. Its 22 miles of navigable water makes it ideal for harbouring large vessels.)

At the time, the UK Government was worried about Napoleon’s European wars, and feared an attack from his armies at some point. French soldiers last invaded UK soil 62 years earlier, further round the Pembrokeshire coast near Fishguard.

It was feared that troops might land on a south or east-facing Pembrokeshire beach, and then attack the docks from land.

The Palmerston Fort designed on St Catherine’s island was originally planned as one of five forts dotted along the coast, mainly at beaches where such landings could take place. Another eleven, in two lines, were also planned to deter an overland attack. However, the only beach-based fort built was this one at St Catherine’s.

There are 74 steps from the beach up to the island’s summit, and then a 10-metre bridge across a dry ditch. Step inside, and the bare walls ooze history from every pore.

Today, large windows fill the three large gun openings on each side, which each housed 7-inch guns. The roof held three more gun platforms capable of housing 9-inch 12-ton guns, one of which was capable of rotating a full 360 degrees.

Built at a cost of £40,000 (approximately £5 million today), it was completed by 1870, yet sixteen years later the Defence Committee decided the fort was incapable of being adapted to meet modern defence requirements. The 9-inc guns were replaced with lighter 7-inch guns in 1892, but by 1898 all the guns had been removed.

Life 3: Private residence

In 1907, the fort was sold to Evan Jones, a tradesman from Llanelli, for a bargain sum of £500. In 1914, it was sold again to the wealthy Windsor-Richards family for £2,000, who converted it into a luxury private residence.

Images from Country Life magazine show the main hall dripping with opulence: marble busts and suits of armour lining the corridors, along with sets of antlers, sword displays and skinned animal rugs. However, work to create this luxury residence couldn’t begin straightaway because . . .

Life 4: WW1 garrison

Between 1914 and 1918, the fort was garrisoned once more as protection for Tenby.

Life 5: Private residence

Now the fort could really thrive as a private residence. Once the refurbishment was complete, it hosted many local society functions, including the Tenby Hunt Ball.

Life 6: WW2

The fort was compulsory purchased in 1940 by the state, and garrisoned again, including by the Home Guard and an RAF detachment. But before the forces could move in, the fixtures and fittings of the private residence needed to be stripped and sold. The job was given to Harrods, who auctioned the fixtures and fittings in 1940.

Life 7: Private residence

After the war, the Government sold the island to a local solicitor, who rented it out. One of its tenants was the author and journalist Norman Lewis.

Life 8: Zoo

In 1962, the island was sold, and by 1968 it opened again to the public as a zoo. It contained over 100 animals, mainly monkeys, an alligator, and even a badger called Winston.

An island might be seen as a perfect venue for a zoo, but the monkeys had other ideas, frequently escaping from their pens and making their way down to the beach, where they would steal hats, scarves, and handbags from tourists sunbathing on Tenby’s Castle Beach.

But they never ran off. The monkeys always returned to their cages at night, knowing they were safe on the island and would be well-fed.

Life 9: TV set

The Zoo relocated in 1979, and the fort lay empty for many years. In 2016, the BBC television series Sherlock used the fort as the setting for a secret Government maximum security facility located in the North Sea, for the episode title The Final Problem.

Life 10: Tourist attraction

Today, the fort is open as a tourist attraction during the summer months. Run by a band of volunteers, tourists can explore the lives of St Catherine’s Fort for themselves at low tides, when the weather permits.

It makes for a truly fascinating visit. For more information about opening times and tide, visit St Catherine’s Fort Facebook page.