From the Celtic period to the Gallic era
Numerous salt-making workshops appeared throughout the upper Seille valley at the beginning of the Early Iron Age, particularly during the 6th century BC. The workshops of this first phase of Briquetage de la Seille are concentrated around Marsal, but can be found as far away as Salonnes, close to the salt springs resulting from the presence of geological faults. The average size of these operations was between 1 and 5 hectares.
The second phase of Briquetage de la Seille corresponds to the end of the Gallic period, from the 2nd century to the 1st century BC. The workshops were now grouped into three major production centres, the largest of which was Moyenvic, ahead of Marsal and Vic-sur-Seille. The average size of the production areas had increased tenfold to several dozen hectares.
The salt production chain
Excavation of the 4th century BC workshop area identified in Marsal ("la Digue") has shown that the salt extraction was preceded by an initial stage in which the brine, no doubt drawn from salt wells, was concentrated and left to settle. The brine was then enriched by washing salty soils, then brought to saturation point in a series of flat-bottomed basins lined with a layer of impermeable clay.
Other, smaller, watertight basins were used as reservoirs for saturated brine, which was used to feed the furnaces. In a second phase, the salt crystals were extracted from the brine and heated in flat-bottomed terracotta basins.
Then, in a third and final phase, the salt obtained was combined in "salt moulds" made of porous earth and moulded using templates; this made it possible to obtain salt blocks of standardised dimensions and weights. At the end of this process, the salt moulds were broken open to release the final product.
Techno-typological developments
During the early phase of Briquetage de la Seille, the salt was extracted in two successive cooking stages: in the first stage, the saturated brine was heated in flat-bottomed "basins" each holding around thirty litres. Then, in a second stage, the salt crystals were packed into flat-bottomed, tray salt moulds, which were used to make oblong salt blocks.
The loads of salt moulds were placed in furnaces equipped with horizontal grates made up of an assembly of round or square-shaped, curved bars made out of terracotta. They were assembled using connecting pieces made of moulded, fresh balls of clay to join the bars to each other and to the walls of the furnace.
A new type of salt mould, which replaced trays, appeared at the end of the 6th century BC. These were vertical, bucket-type vessels, used to make cork-shaped salt blocks.
At the end of the Gallic period, this type of salt mould evolved into elongated shapes such as flutes. These vertical vessels produced salt blocks in the shape of a truncated cone. At the same time, the large curved bars of the early Briquetage de la Seille phase evolved into a single, small bar type with a round cross-section.
