Skilled migrants took their knowledge and expertise of mining and iron-working technology all over the world, together with the distinctive culture which had evolved in the Valleys.
Aeth ymfudwyr medrus â'u gwybodaeth a'u harbenigedd o dechnoleg mwyngloddio a gweithio haearn i bob rhan o'r byd, ynghyd â'r diwylliant unigryw a oedd wedi datblygu y Cymoedd.