Around 20 skulls washed from a Roman burial ground have been unearthed in London.
The "unexpected and fascinating discovery" was made during excavations for the £14.8 billion Crossrail project which has already thrown up incredible finds.
The latest find came while workers were building a utility tunnel at the Liverpool Street station site.
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Working under the direction of Crossrail's archaeologists, the construction workers carefully removed the human skulls and Roman pottery, found in the sediment of the historic channel of the River Walbrook.
The skulls were found below the Bedlam burial ground established in the 16th century, where 3,000 skeletons will be carefully removed during major archaeological excavations next year.
A plan of the original Bethlehem hospital. It has been rebuilt twice in different London locations since.
For safety reasons, the archaeologists have had to leave the archaeology work to the tunnellers as the skulls were up to six metres below ground.
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Roman skulls have been found along the historic Thames tributary the River Walbrook throughout London's history.
This led to speculation they were heads decapitated by Queen Boudicca's rebels during the rebellion against Roman occupation in the 1st century AD.
However, later archaeology suggested that the River Walbrook possibly eroded a Roman cemetery under Eldon Street in the Liverpool Street area and the skulls and other bones had been washed downstream.
The latest skulls were located in clusters indicating they were caught in a bend in the river. The location of the skulls indicates they were washed out of the burial ground during Roman times.
Lead archaeologist Jay Carver said: "This is an unexpected and fascinating discovery that reveals another piece in the jigsaw of London's history.
"This isn't the first time that skulls have been found in the bed of the River Walbrook and many early historians suggested these people were killed during the Boudicca rebellion against the Romans."
He went on: "We now think the skulls are possibly from a known Roman burial ground about 50 metres up river from our Liverpool Street station work site. Their location in the Roman layer indicates they were possibly washed down river during the Roman period."
The tunnellers have also discovered wooden medieval structures believed to have been part of the walls of the Bedlam burial ground.
The Museum of London Archaeology will analyse the finds over the coming months and hope to find out more about the age, sex and diet of the people associated with the Roman skulls.
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Some more Crossrail facts:
- Eight new underground stations at Paddington, Bond Street, Tottenham Court Road, Farringdon, Liverpool Street, Whitechapel, Canary Wharf and Woolwich will be built
- A new surface station will also be constructed at Custom House
- Crossrail will increase the capacity of London’s rail based public transport network by 10 per cent
- An estimated 200 million people will travel on Crossrail each year
- Phyllis (one of the TBMs) is currently under Hyde Park having completed 2.9km of tunnel and is now heading for Crossrail’s Bond Street Station western ticket hall in Davies Street
- At least two-thirds of all Crossrail excavated material, more than 4.5m tonnes, will be used to create the new RSPB nature reserve at Wallasea Island, creating Europe’s largest man-made coastal reserve