sediments. Since the Middle Ages they have been continuously drained by people. In the north, the Marais Poitevin dries up, at the centre there are the valleys of the small river Curé and its main tributary the Virson and in the east the valley of the Mignon. In the south is the marshland of "Little Flanders" (), drained since the 17th century. Together these constitute an important reservoir of fresh water, essential for the agricultural and snail-farming activities of the north of the department. Transport The geography of the plain was always very unfavourable for communications. The region was almost an enclave, and for a long time on the margins of the French kingdom politically as well as geographically. Huge efforts were made to break this geographical isolation. Without doubt the most spectacular was the coming of the railway in 1857, running from La Rochelle and Rochefort to Paris. This line has been repeatedly modernised (made double track, and electrified in 1993 for use by the TGV). The regional railways connecting Nantes to Bordeaux also serve Aunis, passing through La Rochelle, Châtelaillon-Plage and Rochefort. Roads have also been considerably modernised, notably the roads from La Rochelle to Rochefort, from La Rochelle to Niort, the A837 autoroute from Rochefort to Saintes, the viaduct over the Charente at Rochefort, the ring road around La Rochelle, and the bridge to the Île de Ré, all of which are now dual carriageways. The modernisation of communication infrastructure had its heyday in the second half of the 19th century, at the end of the Second French Empire, and economic activity diversified. Agricultural and maritime activities The two principal agricultural resources are intensive arable farming (wheat, maize, oil seed) and livestock farming. Dairy cows have long been the mainstay, but more and more cows and bulls are raised for beef (principally in the marshy areas). Vineyards were virtually abandoned after phylloxera wiped them out in 1876, although there are still some on the Île de Ré. At sea, between the estuary of the Sèvre Niortaise and the north of La Rochelle, mussel farming () has an important place, while Fouras and the Marais d'Yves Nature Reserve are the main centres for oyster farming. La Rochelle keeps its place as a fishing port thanks to its modern port of Chef-de-Baie, but even so fishing is in decline. Reclamation of sea salt from the marshes of Aunis brought