The current production technique in the salt marshes, known as the solar technique, was already in use before the 9th century. The creation of salt works took place over several centuries, and some works from the Carolingian era (751 to 10th century) are still being used intact in Batz sur Mer. Around 1500, the salt marshes made up 80% of their current surface area. Between 1560 and 1660, thanks to the development of sea trade, 2,500 crystallisation ponds or "oeillets" were built. The last salt works were built around 1800. At its peak, the basin contained 22,000 "oeillets".
Good salt workers have always been considered to be honest and hard-working. The salt works were always owned by the upper classes (clergy, noblemen, Duke of Brittany, the King), with the salt workers' salary (a word which comes from "salt") being largely inferior to the value of the product, which itself generated power and taxes.