Henry VIII’s long-lost castle has been found inside another castle

Christopher Moore of the University of Kent discovered an archival report from 1883 stating that building materials from the crumbling Sandown Castle were sent to Dover. There, they were used in the extension of Constable’s Gate — the medieval gate of Dover Castle. Thus, fragments of the 16th-century Tudor fortress are now literally located within the structure of another historic complex.

Henry VIII built three fortresses in case of invasion

Sandown Castle was built in 1539–1540, when Henry VIII was urgently fortifying the south and east coasts of England.

Following the conflict with the Catholic Church and European powers, the king feared an invasion. New artillery forts, designed to house heavy cannons, began to be built along the coast.

Sandown was part of a chain of three fortifications defending the strategically important Downs anchorage off the Kent coast. To the south lay Deal Castle and Walmer Castle. All three forts featured a distinctive design with a massive central core and rounded bastions, allowing fire to be directed in various directions.

Deal and Walmer have survived to the present day.

Sandown was far less fortunate.

The sea gradually eroded the castle

The fortress stood right on the coast and proved particularly vulnerable to storms and erosion.

As early as 1785, the sea breached its moat, after which the structure was deemed unfit for habitation. It was repaired in 1808 and used again during the Napoleonic Wars, and as late as 1855 the castle remained relatively well-preserved.

But following further damage, its fate was sealed.

In 1863, the Ministry of Defence sold Sandown Castle for use as building material. By 1882, a significant part of the fortress had already been dismantled. Today, mainly the foundations, underground elements and small fragments of the structures remain, some of which have been incorporated into the modern coastal defences.

It seemed as though one of Henry VIII’s castles had simply vanished.

In fact, its walls began a new life.

In 1883, the stones were sent to Dover

Christopher Moore specialises in the study of lost and hidden architecture. Working with archival materials and surviving buildings, he discovered an 1883 report stating that materials from Sandown Castle were sent to Dover Castle.

The stone was intended for the extension of Constable’s Gate. The extension was built in 1883–1884 as accommodation for the garrison commander.

The result was an unusual architectural structure spanning several eras.

Dover Castle itself, in its present form, began to take shape under Henry II in the 12th century. Following the sieges of the 13th century, one of the former entrances was closed off, and Constable’s Gate was built as the fortress’s new western gate. More than 600 years later, it was extended – and stone from the Tudor-era Sandown Castle was used for this Victorian extension.

In other words, within a single structure today, a medieval fortress, Victorian architecture and material from Henry VIII’s defensive works all coexist.

The old stones were deliberately used to make the extension look older

It is particularly interesting that the choice of material appears not to have been random.

The historical work *Annals of Dover*, published as far back as 1916, reports that during the extension of Constable’s Tower in 1883, old stones from the dismantled Sandown Castle were used so that the new extension would not contrast too sharply with the ancient structure.

In other words, the Victorian builders had access to virtually perfect material.

Rather than artificially ageing the new masonry, they used genuine stone from another fortress, which by that time was over 300 years old.

Consequently, a fragment of the lost castle was literally concealed within the later reconstruction — in plain sight of the thousands of visitors to Dover Castle.

But the Sandown stones ended up not only in Dover

Moore’s research shows that, following its dismantling, the fortress literally ‘spread out’ across East Kent.

Documentary and architectural evidence links its stone not only to Dover Castle, but also to Eastry Union Chapel, Walmer Castle and the pier head of the second pier at Deal.

Its reuse at Walmer is also confirmed by an official record from Historic England: following the sale of Sandown Castle, its stone was used in the gates of Walmer Castle, as well as in the ornamental gardens and rockeries.

Therefore, whilst Sandown Castle has virtually disappeared in the formal sense, physically, some of its material still exists in several different locations.

This is an example of what architectural historians call ‘spolia’ – the reuse of elements from older buildings in new structures.

In this case, an entire Tudor fortress effectively became a source of architectural details for 19th-century buildings.

The fact itself was known previously — new research has strengthened the evidence

As early as the 1916 *Annals of Dover*, there was explicit mention of the use of old Sandown stone during the extension of the gate in 1883.

The novelty of Moore’s work lies elsewhere. He returned to archival sources, uncovered a report dating directly from 1883, cross-referenced the documentary record with the surviving architecture, and examines Dover as part of a broader picture of the movement of building material from Sandown across East Kent. The University of Kent itself describes the finding as ‘new evidence’, rather than the first historical mention of this connection.

Therefore, the headline ‘lost castle found inside another castle’ works as a metaphor, but literally speaking, the archaeologists did not discover a secret fortress behind a wall.

They traced where the stones from the ruined structure had ended up.

A little more of Sandown itself remains than it might seem

It is also worth qualifying the claim that the fortress has completely disappeared.

Historic England reports that isolated sections of the foundations and underground structures have survived at the original site, including elements of the central tower and two bastions. Part of the ruins is hidden underground or incorporated into modern coastal infrastructure.

Consequently, Sandown Castle exists today in two forms: as a small archaeological remnant at its original site and as reclaimed building material used in other structures across Kent.

That said, its two ‘neighbours’ within Henry VIII’s defensive system have survived in a much better condition. Walmer Castle still retains much of its original 16th-century fabric, whilst Deal Castle remains one of the most distinctive surviving artillery forts from the royal programme of 1539–1540.

The castle has vanished, but its walls have outlived it

And this is the most unusual part of the story.

Sandown Castle was built as a powerful artillery fortification capable of defending the English coast against invasion. But in the end, the structure’s main adversary turned out to be not a foreign army, but the sea.

Three centuries after its construction, the castle began to be dismantled, and its walls ceased to exist as a single structure.

But the stone proved too valuable to be discarded.

As a result, today a person can enter Dover Castle through Constable’s Gate and find themselves standing next to material from Henry VIII’s fortress, without even realising that part of the long-vanished Sandown Castle has been right in front of them all this time.

Source

New research has been carried out by Dr Christopher Moore, a research fellow at the University of Kent specialising in hidden and lost architectural heritage. He cross-referenced archival documents with surviving architecture in collaboration with English Heritage.

A key new piece of documentary evidence was an 1883 report stating that building materials from Sandown Castle had been sent to Dover for work on Constable’s Gate. The extension was built in 1883–1884.

The article was published by the University of Kent on 18 August 2026 under the title“Hidden in Plain Sight: New Evidence Links Henry VIII’s Lost Castle to Dover Castle”.