Archaeologists say finds at the three-acre site may provide the earliest foundation date for Roman London, currently AD 47.
The dig "will transform our understanding" of Roman London, experts told the BBC.
"We have entire streets of Roman London in front of us," Sadie Watson, site director for the Museum of London, said.
The 40-foot deep archaeological dig is thought to be one of the deepest ever conducted in London, experts said.
The site contains "layer upon layer of Roman timber buildings, fences and yards, all beautifully preserved and containing amazing personal items, clothes and even documents," museum staffer Sophie Jackson said.
Tree ring samples from the preserved timber will provide precise dating for Roman London, expected to be earlier than the current figure of AD 47, researchers said.