Dover Castle's original entrance, multiple lost towers and long-gone defensive walls are just some of the remarkable features revealed for the first time by a state-of-the-art digital model of Dover Castle in Kent.

Painstakingly created over 800 hours during research for Dover Castle Under Siege, the model 'restores' the castle as it likely looked in 1216 – before it was besieged and badly damaged in a 'forgotten' civil war which changed the course of English history.

The project was researched by a team of English Heritage experts, including historians, curators and one of the country's leading historical 3D artists.

The 1216 model is central to the creation of Dover Castle Under Siege, a major new experience which opens up the castle as never before.

From 22 July, visitors can explore Dover's medieval and Georgian underground tunnels and casemates with an immersive exhibition.

Visit, and you can see the model and stand close to the spot where the invaders broke through the original entrance.

New access through the tunnels and out onto the great earthwork defence, known as the Spur, provides a magnificent panoramic view of the castle to visitors for the first time.

Between 1215-1217, a civil war raged in England.

French soldiers, led by Prince Louis 'the Lion' (son of King Philip II of France), fought alongside English rebel barons against King John.

In 1216 Dover Castle, which remained loyal to John, was a formidable fortress, having been massively extended and strengthened over the previous 40 years.

Its layered defences offered only one practical route for an attack: at the northern tip where the main gate of the castle stood.

French and rebel forces broke through into the outer bailey and an epic, bloody struggle for control of the castle ensued.

Hundreds of knights and soldiers in chain mail swung swords, axes and maces, and dug tunnels to undermine the gate and gain entry, but the castle's defenders, led by the great warrior Hubert de Burgh, would not be conquered.

The new digital model shows where the entrance originally stood, defended by King John's twin-towered gatehouse, from which a wooden bridge crossed the deep outer ditch onto a barbican, a fortified strongpoint defending the approach to the gate.

Now, for the first time in almost 1,000 years, there is a vision of Dover Castle in a brief moment of calm before the siege.

Paul Pattison, English Heritage's Senior Properties Historian, said, 'When you see the model, Dover Castle almost rises from the ashes of the siege in 1216; the level of detail is astonishing.

'It has taken us months of research, deliberation and difficult decision-making to be able to produce this model. From historical records, plans and maps, and archaeological, topographic and laser surveys – we've left no stone unturned in making this model as accurate as possible.

'After the siege, the castle was massively and expensively re-fortified, attempting to ensure it could never be breached again.

'Many of those changes we can still see today, from the imposing new entrances at Constable's Gate and Fitzwilliam Gate, to a network of underground tunnels.

'As Dover Castle Under Siege opens, I can't wait for the public to experience walking underground and out onto the Spur for the first time, and to imagine those who fought in that same spot centuries ago.'

Bob Marshall, English Heritage's Architectural Illustrator, said, 'Creating this digital model of Dover Castle was an intimidating prospect mainly given the sheer scale of the castle – it's the country's largest in terms of square acreage.

'But by combining all of the archaeology and archival research with detailed surveys, I was able to painstakingly create this model to high standards of accuracy, which has helped to inform the entire new experience.

'I think this use of technology will continue to change the way so many people think of Dover Castle. It hasn't stayed the same over hundreds of years. Each era, from medieval to Georgian to the Second World War, has left its mark.'

• Dover Castle Under Siege opens to the public on 22 July 2024.