ARCHAEOLOGISTS have begun a dig to attempt to discover the mystery behind one of the country's most important Prehistoric monuments.

A National Trust team began work at Belle Tout, on top of the Seven Sisters cliffs, on Tuesday and will be excavating trenches close to the cliff edge.

Archaeologists have said this will be the last opportunity to solve the mystery of the site before the cliffs fall into the sea.

They hope to find evidence of an early Bronze Age settlement complete with prehistoric monuments close to where there is now a lighthouse and cafe.

It is already known that there is a huge outer earthwork, nearly a mile long, but archaeologists have yet to arrive at a date for when the hilltop enclosure was built.

Previous finds are from different eras including Prehistoric flintwork and early Bronze Age pottery.

What sets this project apart from previous excavations is the application of new scientific techniques such as LiDAR laser scanning, environmental sampling, Optical Stimulated Luminescence (which measures the last time an object was exposed to light) and analysis of microscopic snails, which only exist in certain habitats and give clues as to the ancient landscape.

Tom Dommett, National Trust Archaeologist, said: "This is the gold standard in terms of archaeology research - and rightly so - as conceivably it will be the last chance to undertake this work before the areas are gone due to coastal erosion.

"We have worked closely with Historic England and with Natural England to enable this important project to take place in such a sensitive area and are hugely grateful to our team of volunteers."

More than two dozen volunteers will work on the dig every day alongside experts and professional archaeologists.

The team will be taking care not to work any closer than 10 metres from the edge, as the cliffs can be unstable in places with hidden undercuts.

Mr Dommett added: "This is one of the most ancient and fascinating archaeological sites in Sussex.

"The site at Belle Tout is already a scheduled ancient monument – a site of national importance. It has been the subject of archaeological work for the last 100 years, but despite this it remains a mystery.

"We don't know for sure how much we've lost over the last 6,000 years due to coastal erosion, but there is a good case for saying it was the largest prehistoric enclosure in the country.

"We will be investigating the heart of the settlement, likely to be Bronze Age."

Members of the public are invited to visit and take part in free tours, which are open daily.

People can see the archaeologists in action, take a tour of the trenches with volunteers, examine the finds and learn more about this special, historic landscape.