Kent's forts were at the forefront of the nation's defences against everyone from the Romans to the Nazis, but many have been transformed in later life.

Former tyre dumps and exclusive penthouse apartments with panoramic views form part of these looming buildings' fascinating histories, writes Lynn Cox.

Fort Clarence, St Margaret's Street, Rochester. Now exclusive apartment homes

Work on Fort Clarence started in about 1808 and was completed within four years.

It was built to stop invaders gaining access to the River Medway and had a brick revetted dry ditch running between a guardroom on the Rochester-Maidstone Road to a tower alongside the river.

The fort has a massive red brick keep, in the style of a medieval castle, which served as a gun tower and observation post.

The dry ditch running across Margaret's Street was crossed by a drawbridge through a substantial guardhouse in the form of an arch, but this was demolished in the 1930s.

After 1815, the fort served a variety of purposes, including a a 'lunatic' asylum and military prison, with a brutal corporal punishment routine according to newspaper reports from the time.

The fort was used by the garrison artillery throughout the First World War as a recruiting centre, then afterwards a Territorial and Volunteer Reserve centre was built beside it and the main barracks site was wound down.

Then, during the Second World War, Fort Clarence was used by the Home Guard as headquarters and a large aircraft factory was built underneath by Short Brothers, whose main factory sat close to the River Medway below the fort.

After the war ended, the site became derelict but in the 1960s GPO (now BT Group) were based there.

The communications firm demolished the barracks, filled in large parts of the moat and demolished the Maidstone Road guardroom.

A brick gun tower and a section of ditch from St Margaret's Street into gardens opposite remain today. Below the gardens, which are publicly open, is a sally port with sealed-up door.

The door used to connect with the tunnel which led to the Medway Tower, which has long since been demolished. The underground factory entrance has now been built on and the factory front which served it was destroyed after Shorts left in 1949.

Since then the site, now a Scheduled Ancient Monument, has changed hands and been converted into four apartments, with the outside of the tower restored and a modern structure added to the roof.

In 2017, one, two-bedroom penthouse apartment at the site, which has its own private roof terrace with stunning panoramic views of the River Medway and central Rochester and beyond, was on sale for offers in excess of £500k.

Take a look inside the exclusive apartments

The tunnel complex is sealed off but maintained by English Heritage and as late as 2000 developers reportedly found war-time aircraft components in the parts they visited.

Fort Pitt, Fort Pitt Hill, Rochester/Chatham. Became a hospital and is now a grammar school

Fort Pitt was built in the Napoleonic era on high ground between the boundary of Chatham and Rochester.

Proposals to build a fort there were first put forward in the 1790s but it was finally built between 1805 and 1819.

It was named after Prime Minister William Pitt and was part of the defences overlooking the River Medway.

Fort Clarence, Fort Amherst and the Great Lines were visible from the fort and it provided a defensive ring to protect Chatham's dockyard.

The fort had red-brick walls with a bastion at each corner, and was surrounded by a 15-foot trench.

Originally it included a number of buildings which have now been demolished, including a tower or keep which was removed in 1910 and a large blockhouse for 500 men.

It also had two towers, one on each flank, named Delce and Gibraltar. In 1879 Gibraltar Tower was demolished, while Delce Tower, by then a ruin, was razed shortly afterwards. The blockhouse was knocked down in the early 1930s.

Because of the end of the Napoleonic Wars the site was never actually used as a fort. However, soldiers were sometimes based there, including in 1815 when the wounded from the Battle of Waterloo were housed in its buildings.

In 1828 it became a base for injured soldiers and was made a military hospital from 1832.

An 'asylum for insane soldiers' was added in 1847 and by the 1859s the site was a major military hospital, with most of the soldiers injured abroad looked after there until they were fit to be discharged.

Queen Victoria came to Fort Pitt on three separate occasions in 1855 to visit soldiers wounded in the Crimean War.

In 1860 Fort Pitt was selected by Florence Nightingale as the initial site for the new Army Medical School, before this moved to Netley near Southampton in 1863.

The site continued as a garrison hospital and in October 1914 King George V and Queen Mary visited, meeting servicemen wounded in the First World War.

This included five German Naval officers and at least 70 German prisoners.

Once recovered they were held in the blockhouse until the end of the war. The hospital finally closed in 1919.

Then, 10 years later, the Chatham Education Board bought the site from the War Office and it was converted into a Girls' Technical School.

The school, which is now known as Fort Pitt Grammar School, remains on the site and has added a number of new buildings over the years.

The neighbouring University for the Creative Arts (UCLA) building occupies the old blockhouse site and some of the original brickwork remains visible at the sides of the building.

The Music House, which was the former 'insane asylum', in the school grounds and the 'Crimea Wing' teaching block are listed buildings, with some of the old hospital ward numbers still visible on the Crimea Wing's walls.

Several other buildings date back to its hospital days and possibly earlier.

However, part of the old hospital building was destroyed in a fire in 1973.

The site continues to be of national historical significance.

Sandgate Castle, Sandgate, Folkestone. Now a private home

Sandgate Castle was built as an artillery fort by Henry VIII between 1539 and 1540.

It formed part of the King's Device programme to protect England against invasion and defended a vulnerable point along the Kent coast.

When first built it had a central stone keep, three large towers and a gatehouse and was fitted with 142 firing points for cannons and handguns.

It was taken by Parliament in 1642 at the beginning of the first English Civil War, but was seized by royalist rebels during the second civil war of 1648.

Later between 1805 and 1808, the castle was redesigned during the Napoleonic Wars.

Its height was reduced and its keep was turned into a Martello tower and it was armed with 10, 11kg guns and could hold a garrison of 40 men.

During the early 17th century the castle suffered damage from the sea and by the middle of the 19th century, the receding coastline had reached the edge of the castle walls.

Because of the cost of any repairs, in 1888 the government decided to sell off the site and it was purchased by a railway company, but was later passed to a private owner.

By the 1950s, the southern part of the castle has been destroyed by the relentless waves, but the remaining parts of it were restored between 1975 and 1979 by a couple who turned it into a private home.

Today, the castle remains in private ownership and is protected under UK law as a Grade I listed building. New apartments have been built alongside it which are similar in shape to what is left of the castle.

Fort Horsted, Primrose Close, Chatham. Now a business centre

The fort is the largest of the Victorian Chatham forts.

Work started on it in 1879 and was completed by 1889.

It was built in the Horsted Valley, south of Chatham and is a late 19th-century Land Fort, one of six constructed around Chatham and Gillingham to protect the dockyard from attacks.

It was named after the local hamlet, which in turn is speculated to have been named after the legendary Saxon warrior Horsa who was killed at nearby Aylesford while fighting the British.

Plans for a fort on the site were originally proposed in 1860 along with other land defences in the area, but as part of a cost-cutting exercise only coastal defences on the River Medway were completed.

It was not until the mid 1870s that revised plans were accepted to build Fort Horsted, which included the construction of a prison at Borstal - now HMP Rochester - along with a further three forts, Borstal, Bridgewood and Luton.

Fort Horsted was built almost entirely out of concrete and was topped with chalk and earth so none of the concrete was exposed from the outside, except from the back.

Although the original plans proposed fixed armament, by the time it was finished there had been a shift to moveable guns.

In the end it was decided the fort would not be armed unless an attack threat happened and then moveable field artillery would be used.

By 1910 Fort Horsted was deemed obsolete, but it formed part of Chatham's land defences in both the First and Second World Wars.

During the first conflict, brick emplacements and a pillbox were built on the ramparts, and fixed anti-aircraft guns of an early type were installed.

Over the next few decades, the fort had a variety of owners and tenants including Kent County Council, Ford UK, Boxwell Developments, the Biber Group, The Rootes Group, the Rochester Motor Company and Fort Tyres.

In 1972 an application was made to demolish it and build 120 new homes, but after a public inquiry it was deemed an ancient monument of great local interest and the homes were never built.

In 1976 when it was owned by a German company, Fort Tyres, an estimated 100,000 tyres were dumped on top of the site, in the tunnels and the moat.

In July that year, a massive fire broke out and thick black plumes of smoke could be seen for miles around.

At the peak of the blaze more than 50 firefighters fought the flames and it actually burnt for weeks.

By the early 1990s it was all but deserted and derelict.

English Heritage and the Environment Agency issued an enforcement notice on its owners to clear the site of all its tyres.

Instead it was put up for auction and was bought by Avondale Environmental Services Ltd in 1997.

English Heritage continued to support Avondale during the next four years as it cleared the tyres and brought the Fort back to a habitable condition.

In April 2007, it became Fort Horsted Business Centre and was officially opened for firms to lease out units.

Rooms and tunnels at the site can also be rented out for private parties and prices vary depending on event, time of year and duration of event.

Avondale Environmental Services is still based at the site, while others businesses that occupy units there include, Fort Horsted Properties Limited, White Cross Care Ltd, Forces Family Finance Ltd and Every Family Finance Ltd.

Ghost hunts are also sometimes held at the site, which is still a scheduled monument.

To find out more about other Kent defences, which warded off everyone from the Romans to the Nazis, but have now decayed or been swallowed by the land they once protected, click here.

To read more of our in-depth features click here.

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