The drones are also used to survey the cliff face itself which, due to previous collapses, already provides a cross-section of the fort. “We’ve got one image very clearly showing the ditch and bank of the enclosure,” said Mr Sygrave.

Whatever the results, time and tide are working against his team.

On average, the coast at Seaford is retreating by 50 centimetres (20 inches) a year. That figure, however, masks a pattern of large cliff collapses followed by months or even years of stasis. The UCL team cannot predict when the chalk might next give way, but it could take with it another large chunk of the fort. 

Large chunk of cliff collapsed last year

In March 2021, a large section of the Seaford Head cliff face collapsed following heavy rain, leaving behind an enormous mound of debris reaching into the seawater. Elsewhere on the clifftop, large cracks have appeared, portending further losses. That prompted English Heritage to place it on the Heritage at Risk register.

“Every time that there’s a section of cliff that’s lost, it’s not just the material that’s lost in that cliff collapse. There’s also the area behind it, because you can’t safely work within the first 10-20 meters of the cliff,” explained Mr Sygrave.

Climate change, meanwhile, is likely to accelerate this process. Increasingly rough weather conditions and rising sea levels are all expected to eat away at Britain’s coastline and the ancient monuments dotted along it. 

Marcus Jecock, a senior archaeological investigator and coastal lead at Historic England, said: “Coastal erosion is not a new threat, but climate change is accelerating the rate at which erosion is happening and thereby the rate at which archaeological sites of all types that exist around our coasts are being lost – often without proper record.”