Axes from the Ice Age used by mammoth hunters when the North Sea was dry have been found from under the water off the Norfolk coast.
Most mammoths died out at the end of the last Ice Age
Dutch amateur archaeologist Jan Meulmeester found the 100,000-year-old hand axes in gravel dredged from eight miles (13km) off Great Yarmouth.
Bones and teeth were also found along with the 28 axes.
Man used to roam the area now covered by the North Sea using flint tools to butcher animals such as mammoths.
The axes date to the Palaeolithic (or Old Stone Age) era. Experts said the discovery offered rare evidence of life before the North Sea existed.
Phil Harding, of Wessex Archaeology and Channel 4's Time Team, described the findings as "massively important".
"Although we don't know their precise date, we can say that these hand-axes are the single most important find of Ice Age material from below the North Sea," he said.
"In the Ice Age the cold conditions meant that water was locked up in the ice caps. The sea level was lower then, so in some places what is now the seabed was dry land."
Mr Meulmeester regularly searches for mammoth bones and fossils in sand and gravel delivered by construction materials supplier Hanson to a Dutch wharf at Flushing in the Netherlands.
It took him three months to collect the axes, but only realised their significance last month.
English Heritage is working with its Dutch counterpart to evaluate the finds and is co-operating with Dutch authorities to develop a research programme for the submerged pre-history of the North Sea.