Near the Luxembourg border of Belgium the River Lesse plunges into the limestone heart of the Ardennes mountains. Before it emerges again it passes through miles of echoing stalactite-hung caverns which for a long time have been one of Belgium's chief tourist attractions.

But for even longer the caves have been a place of refuge, where refugees have left 5,000 years of debris behind them on the river bottom making this one of Europe's richest and most unusual underwater sites.
Chronicle invited three distinguished British archaeologists - Professor Barry Cunliffe, Professor Colin Renfrew and Dr Anna Ritchie - to spend a day with the divers and discuss their finds as they were brought up dripping from the river bottom.

Written and introduced by Magnus Magnusson