Saltworks from the Roman era (1st–5th centuries)
Urban centres developed at the beginning of the 1st century AD at the sites of the major Gallic production centres of Marsal, Moyenvic and Vic-sur-Seille. The technique of extracting salt in clay furnaces was abandoned. The brine was now heated in flat-bottomed metal basins, or salt pans. The Marsal production centre (Marosallum) was linked to the main road between Metz (Divodurum), the capital of the Mediomatric city, and Strasbourg (Argentorate), where large Roman army forces were massed on the border with Germania.
At the end of the 1st century AD, a network of large rural estates developed on the hillsides bordering the valley. The recorded density is one establishment, on average, per square kilometre. Lavish villas began to appear in the vicinity of urban centres: that of "Sauvageon" in Moyenvic was adorned with colonnades and marble cladding.
On the outskirts of the valley, a major religious complex developed at the end of the 1st century AD in Tarquimpol (Moselle). This monumental complex, which included a large temple and an entertainment building, must be indicative of a sacred place at the source of the Seille, which has been frequented since Gallic times.
Merovingian and Carolingian saltworkers (6th–11th centuries)
The urban centres founded in the Gallo-Roman period continued to exist beyond the end of the Roman Empire. Merovingian coin workshops were in operation in Marsal (Marsallo Vico), Moyenvic (Mediano Vico) and Vic-sur-Seille (Bodesio Vico), and probably also at Salonnes (Salionno). They serve as evidence of the wealth and power that salt from the Seille continued to bring.
There is written evidence of salt production in Marsal and Vic-sur-Seille from the end of the 7th century. The salt production centres of Marsal, Moyenvic and Vic-Sur-Seille have been clearly identified since the Carolingian period. There is archaeological evidence of occupation during this period in Salonnes, confirmed by texts that mention the existence of the village of Courcelles (Curcella), which neighboured Salonnes at the beginning of the 9th century.
Rivalries in the medieval and modern periods (12th–18th centuries)
The medieval period was a period of growth and instability for the saltworks in the Seille valley. They suffered as a result of the feudal wars of the 15th century, which pitted the Dukes of Lorraine against the Bishops of Metz for control of salt production.
The period between the 13th and 14th centuries was marked by the development of the fortified urban centres of Marsal, Moyenvic and Vic-sur-Seille. Vic was elevated to the rank of episcopal town and became the residence of the bishops of Metz. A series of castles were built or rebuilt. Vic Castle, which seems to have been built in the 11th century as a residence for the Duke of Lorraine, was (re)built in the 13th by the Bishop of Metz. The "Châtry" castle mound in Vic-sur-Seille appears to date from the end of the 13th century.
At this point, the Salonnes peat bog underwent a third and final phase of intensive deforestation, which seems to have coincided with the development of the medieval saltworks in the Seille valley, between the 13th and 14th centuries.
After the 16th century, advances in artillery led to the Italian-style fortification of the towns of Moyenvic and Marsal. At the end of the Thirty Years' War, Marsal, now owned by the French, was fortified by Vauban. The great royal saltworks at Moyenvic became the major salt production centre in the Seille valley. At the end of the 18th century, the over-exploitation of forests linked to the crisis in the salt industry led to major environmental problems. These combined effects of these phenomena exacerbated social inequalities, in a general climate that saw the collapse of the French Revolution.
