Digs on the site of the London 2012 Aquatics Centre have revealed evidence of an Iron Age settlement. Fourth-century pottery and a Roman coin have also been found elsewhere on the Olympic Stadium site.
The finds will go on to form part of the Museum of London's collection.
The first Londoners lived in thatched circular mud huts on the site that will eventually boast a Zaha Hadid designed Aquatics Centre. They fished in what is now the River Lea.
Pots they would have used to cook their fish have also been discovered.
The Roman Coin and pottery were found buried behind a wooden river wall that may have been built and used by the Romans. The coin is dated to AD 330-335, the time of the Roman emperor Constantine II.
Archaeologists are dating the woodwork and trying to establish how the finds link to evidence of Roman activity in the Hackney Wick area, which would have overlooked the Lea Valley in the 4th century. This is the first evidence for Roman activity associated with the rivers of the valley itself.
ODA Chief Executive David Higgins said: "We are taking this opportunity to tell the fascinating story of the lower Lea Valley before it is given a new lease of life for the Games and future generations.
"It is a story of change and transformation dating back centuries. The archaeological work has been long planned in conjunction with our programme and will not cause any delays."
The ODA has invited Museum of London archaeologists and Pre-Construct Archaeology (MoLAS-PCA) to look for evidence of the original prehistoric Londoners right through to Roman, Viking, medieval and relatively recent industrial and military activities on the Olympic Park site.
"They are also charting the topography of the site to build a picture of how the land and waterways have developed and how climate change has affected the area.
"Trenches are being dug and investigated on the sites of the permanent venues and infrastructure. Interesting remains will either be photographed and recorded or removed to form part of the Museum of London's collection.
"The archaeological research is interlinked with work preparing for construction and shows that nothing of national importance requiring preservation on site is expected to be found," he said.