Salt was extracted in two different ways:
Briquetage is based upon evaporation of seawater: seawater is poured over a tower-like construction of porous pottery or wood. Sun and wind evaporates the water leaving a concentrated brine which can be crystallized on fire.
With Moernering saltextraction takes place by burning peat or salt-loving plants, dissolving the ashes in (sea)water and evaporation of the remains.