Archeologists studying aerial photos of the coast of Wales found a 1000-year-old fish trap lurking beneath the waves.
The unique shape of the rock structure helped the Normans trap fish without boats or anything at all. All they had to do was wait for the tide to go out and hundreds of fish would be trapped behind the rocks.
Nets were placed at a narrow exit to catch the fish on their way out. Fish weirs were so effective that overfishing led to a provision in the Magna Carta banning them in rivers.
All fish-weirs shall be removed from the Thames, the Medway, and throughout the whole of England, except on the sea coast.