Salt is essential to human survival. In Central Europe, the Celts were among the very the first salt miners, and grew wealthy from establishing an international salt trade. So, where did the early Irish get their salt?
There’s a fascinating chapter on Celtic salt miners and the European salt trade in general in Mark Kurlansky’s excellent book, Salt: A World History. He details how the Celts were innovators, who realized the importance of salt, and developed the means to mine it successfully in the Alps and other central European locations. They became very wealthy through the international salt trade, and their traders travelled all the way to the Middle East, North Africa, and China.