Grosseto is located in the alluvial plain of the Ombrone river, at a distance of 14 km from the Tyrrhenian sea. The town was probably first settled in the 8th century, and grew in importance because of the trade in salt, that was obtained in salt pans in the now reclaimed lagoon that covered most of the area between Grosseto and the sea. Because of its wealth, the town was disputed between Siena and Florence in the 13th and 14th century. By the time however that the Sienese finally managed to assert their dominance over the city in 1328, its tide was already turning because of the silting up of the lagoon, robbing Grosseto of its salt revenues. Grosseto was largely depopulated, and became an extremely unhealthy place because of the malaria in the marshy areas surrounding the town. Despite several attempts to drain the marshes, the town only started to grow again in the 19th century.