- Construction workers digging a tunnel in London have found about 20 Roman-era skulls
- The workers were digging a tunnel for the Crossrail rail project spanning the city
- Archaeologists believe the skulls were washed down stream from an old burial ground
- More than 10,000 archaeological items have been found since the project began in 2009
(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.
Read more: Rail excavation unearths suspected 'plague pit'
View of excavations at Bloomberg Place, which is currently the largest commercially funded development project in the world. The site embraces the longest stretch of the Roman Walbrook left in the City. 
A complete amber Gladiator amulet. Seven meters of archeology have been excavated, including remains covering the entire Roman occupation of Britain -- from the mid 40s AD to the early 5th century. 
A Roman bull plaque. Ten thousand accessioned finds have been discovered at the site. This is the largest assemblage of small finds to have ever been recovered on a single excavation in London. 
A Roman copper-alloy brooch. 
A Roman iron knife. 
A mystery leather item. This site has supplied the largest quantity of Roman leather to have ever been unearthed in London. 
Roman copper-alloy plate brooch with blue enameling. 
An inked Roman letter. Over 100 fragments of Roman writing tablets have been unearthed, including an affectionate letter. 
A ceramic oil lamp depicting a stag. Approximately 700 boxes of pottery fragments will be analyzed by MOLA -- Museum of London Archaeology -- specialists. 
Complete Roman ceramic beaker. 
Roman leather carbatina (a shoe.) 
Roman fist and phallus. The largest assemblage of fist and phallus good luck charms from one site was discovered. 
A bone sword handle. 
A Roman woven basket. Some 3,500 tonnes of soil have been excavated by hand. That amounts to 21,000 barrows of spoil (soil). 
A Roman tiled floor. Some 75,000 man hours have been spent excavating and recording the extraordinary archeology on site. 
Timber foundation beams from a Roman building. 
A Roman timber drain. Complex Roman drainage systems used to discharge waste from industrial buildings into the Walbrook River. 
Mithras column, part of a previously undiscovered section of the Temple of Mithras. The Temple and finds from the current excavation will become part of a publicly accessible exhibition within Bloomberg's European headquarters. 
The first excavation of the Temple of Mithras excavation in 1954 by eminent archaeologist W.F. Grimes. The discovery was perhaps the most famous excavation of the 20th century, with hundreds of thousands of people flocking to see the work unfold. 
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Pompeii of the north 
London's hidden past uncovered by project 
Black Death 'plague pit' found in London 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.
Read more: London dig turns up slice of Roman life
"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.
Read more: Body found under parking lot is King Richard III
