Huge undersea wall dating from 5000 BC found in France
They think it could be from a stone age society whose disappearance under rising seas was the origin of a local sunken city myth.
The 120-metre (394ft) wall – the biggest underwater construction ever found in France – was either a fish-trap or a dyke for protection against rising sea-levels, the archaeologists believe.
When it was built on the Ile de Sein at Brittany's western tip, the wall would have been on the shore-line – between the high and low tide marks. Today it is under nine metres of water as the island has shrunk to a fraction of its former size.