The Celts originated (="were born") in Central Europe, in the Alps. It was a strong people who had salt (important to keep food)from the mines in the mountains. They could exchange things with no problem, because big rivers start in the Alps. Many place-names everywhere in Europe were given by the Celts ("Mayenne"= "the dark waters"). We know about the Celts by the Greeks and the Romans.

Julius Caesar knew the Celts and he tried to conquer them when he invaded Gaul (= today's France). So many Celtic tribes crossed the Channel and settled in Britain. Some stayed in Brittany, in France.

But Celts from Britain helped their cousins on the continent to fight Caesar, and he didn't like it at all!!!

but