ARCHAEOLOGISTS have unearthed a Napoleonic era watchtower at the start of a dig into threatened Bronze Age burial mounds on the Jurassic Coast.

The National Trust (NT) team is digging into 4,000-year-old earthworks at Charmouth’s Golden Cap to record their history before they slip into sea.

So far they have unearthed the 18th century watchtower built to provide early warning against a French invasion and watch Channel shipping but will be digging deeper into the mounds.

NT archaeologist Martin Papworth said: “These burials are an important feature of the landscape of Dorset and have a valuable story to tell.

“But the archaeological information contained in the barrow group can only be preserved through excavation and record.

“Total loss of the group through cliff collapse is expected in the next 50 years.

“The barrows are scheduled monuments and Engli-sh Heritage have granted permission for the National Trust to excavate the most vulnerable parts of the barrow group.”

The burial is one of a line of four burial mounds visible as earthworks on the summit of Golden Cap, the highest point of the coast path through Dorset.

It is already close to the cliff edge, which at that point is near vertical, making the chance of it being lost soon to a landslip quite high.

The excavations are planned to take three weeks. The Napoleonic era watch station was built on the summit of Golden Cap in the late 18th Century to watch shipping in the channel.

The builders of the watch station used some stone from the burial mounds to create a flat platform and left behind a few traces of their presence.

Items uncovered include the fragments from a large food bowl and some badly eroded coins and buttons.

With the Dorset coast eroding at a rate of about one metre a year, the burial would originally have been build over two miles from the coast.

In June 1992, a trench was excavated across the south-west barrow. It was found that 30 per cent of the barrow had already been lost through coastal erosion.