Unlocking Roman London's underground secrets: Roman skulls unearthed at £14.8bn Crossrail project site

Bones may have been washed from a nearby burial site along River Walbrook

Archaeologists are always prepared for the unexpected when working in subterranean London - known for its fascinating combination of ancient tombs, bomb shelters and derelict Tube stations. And yesterday was no exception, with experts unearthing 20 ancient skulls under the streets of the capital.

The "unexpected and fascinating" find was made during work on the £14.8bn Crossrail project, which is cutting through much of the capital's underground history.

Archaeologists discovered the Roman skulls, along with pieces of Roman pottery, while excavating a channel of the ancient River Walbrook which runs, underground, through the City of London near Liverpool Street train station.

"This discovery reveals another piece in the jigsaw of London's history," said lead Crossrail archaeologist Jay Carver. "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."

The truth is probably less grisly; as they were located in clusters, indicating they were caught in a bend in the river, added Mr Caver, it means they were most likely washed downstream from an ancient Roman cemetery under Eldon Street in the Liverpool Street area Due to safety concerns, Crossrail's archaeologists have had to leave the early stages of archaeological work to the project's specialist tunnellers, as the skulls were up to 6m below ground. While excavating the skulls the tunnellers also found more recent wooden structures from the medieval period, believed to have been part of the walls of an ancient burial ground.

Professor Mary Beard of Cambridge University has previously called the area "tremendously important" for the study of Roman history, while Michael Marshall of the Museum of London Archaeology labelled the Walbrook site as "one of the most important in the north-western provinces of the Roman Empires".

The river runs from Finsbury, on the northern edge of the City of London, to the River Thames by Cannon Street railway station, and has long been known to be something of an ancient rubbish dump. In April this year an unprecedented haul of 250 leather shoes, plates and wooden writing tables was uncovered near Mansion House Tube station in the biggest find of Roman antiquities ever made in the capital.

It has been a busy year for Crossrail's archaeologists in the capital after they discovered dozen of skeletons from a suspected Black Death burial ground under Charterhouse Square near Barbican station in March. The "death pit" was just 5.5m wide and lies just outside the ancient walls of London in an area referred to at the time as "no-man's land".

Nearby at Liverpool Street a rare 16th-century gold coin that was used as a sequin, similar to those worn by royalty, was found in August, while further south North Woolwich archaeologists working under Mr Carver found a Mesolithic "tool-making factory" which included 150 pieces of flint, dating from some 9,000 years ago.

Next year archaeologists will, in major archaeological excavation, remove 3,000 skeletons from the 16th-century Bedlam burial ground to make way for the train line, which will link London to the rest of the south-east of England via a line to Maidenhead, Berkshire, in the west to Shenfield, Essex, and Abbey Wood, London, in the east. Since construction started on the massive scheme in 2009 more than 10,000 archaeology items, spanning more than 55 million years of London's history, at over 40 of its construction sites have been discovered.

Given this, the haul of skulls in the City of London isn't "totally surprising" said Mr Carver. He added: "Roman skulls have been found along the length of the River Walbrook and we were aware that this river likely passed through our worksite."

Paul Talling, author of London's Lost Rivers, who runs guided tours of London's underground rivers, also isn't surprised by the find: "Ancient artefacts are discovered in London's lost rivers all the time. It's just that we aren't always aware of the ancient history of the rivers below out feet."

The area of the modern City of London was heavily colonised by the Romans soon after the second invasion of Britain by the Emperor Claudius, in 43AD. Crossrail's contractor, Museum of London Archaeology, will analyse the finds to confirm their origin over the coming months but Mr Carver is convinced they are Roman. "Based on the deposits where we have found them, which are in layers of river silts and gravels that seem to fill the Walbrook River channel and the associated finds of Roman pottery we can be pretty certain," he said.

For further reading:

Crossrail tunnel project uncovers ancient burial ground - including Bedlam patients