Located in southern Vendée, between Luçon, Fontenay-le-Comte, Niort and La Rochelle, today’s Marais Poitevin owes very little to nature, even though the Bay of Aiguillon, where it meets the ocean, has been an officially designated nature park since 1996.
The story began at the end of the last ice age, when a general rise in sea levels created the Gulf of the Pictons in this region, named after the Gaulish people who inhabited its shores. The gulf gradually filled through two natural sedimentation processes: deposits brought in by the sea and river-borne alluvium. The term bri denotes a bluish clay sediment from the Gironde and Loire, carried by ocean currents. This layer is now around ten metres thick and forms the sediment of the Bay of Aiguillon. As the gulf gradually silted up, the ocean’s influence declined, offset by inflows from a network of rivers that emptied into the Sèvre Niortaise. As the environment became less saline, plants proliferated, creating peat bogs farther east through the decomposition of vegetation such as willows, ash trees, reeds and rushes. Together with the clay soils, these peat bogs form the surface layer of today’s marshes and account for their exceptional fertility.
Early human intervention ---------------------------------
Until the beginning of the Middle Ages, the coastal marshlands, regularly flooded by the tides and river inflows, remained unused. The local lords had little interest in them and ceded these lands, described as “rotten”, to Benedictine monks. The monks built their abbeys around the gulf and began drainage work in the late 10th century. The proximity of the ocean allowed them to establish highly profitable salt pans. Around their abbeys, they built rings of dikes within which rainwater was collected and drained away, protecting the land from flooding and making cultivation possible. These modest works were destroyed during the Hundred Years’ War (1337–1453) and later during the French Wars of Religion (1562–1598).
The promulgation of the Edict of Nantes (1598) by Henry IV restored peace. To combat the famine caused by decades of war, the king launched an extensive marsh-drainage programme to increase the area of arable land. With the French lords ruined, the sovereign turned to Flemish and Dutch investors, who brought both capital and hydraulic expertise. The engineer Humphrey Bradley (1584–1639), renowned for his work removing sand from the port of Dover and draining the Fens (Great Britain), was appointed “master of the dikes and canals of the kingdom” in 1599. His remit extended “to all the fens and marshes of France, whether they belong to the royal domain, the Church, the nobility or the Third Estate”. The engineer and his associates retained this monopoly until 1639.