(CNN) -- Clusters of Roman skulls have been discovered deep below London's Liverpool Street by construction workers digging a new rail route through England's capital.
Tunnelers working on the Crossrail project found about 20 skulls, deep beneath the 16th century Bedlam burial ground in the center of the city, Crossrail said in a statement.
The human skulls -- as well as fragments of Roman pottery -- were found in sediment of the historic river channel of the River Walbrook, a tributary of the River Thames, it said.
Roman-era skulls had been found along the path of the River Thames throughout London's history, fueling speculation they were the heads of the victims of rebels fighting under Queen Boudicca against Roman occupation, lead archaeologist Jay Carver said.
"We now think the skulls are possibly from a known Roman burial ground about 50 meters up river from our Liverpool Street station worksite," he said. "Their location in the Roman layer indicates they were possibly washed down river during the Roman period."
Crossrail said tunnelers at Liverpool Street also discovered medieval wooden structures, which archaeologists believe may have formed part of the Bedlam cemetery walls.
About 3,000 skeletons previously discovered at the Bedlam burial ground are set to be relocated next year.
The Museum of London Archaeology will analyse the finds, which are the latest in more than 10,000 archaeological items found across 40 project construction sites, Crossrail said.