Zwin

Starting 2800 years ago, climate change and inland deforestation caused increased drainage in the peatlands. As a result, gullies began to cut in and increased tidal space behind the coastal belt. This incision created an open tidal channel landscape with "islands" of older salt marsh and peatlands. The dune belt and cover sand ridges along the edges of the area formed part of a coastal defense line during Roman times. From the settlements, the landscape was drained for small-scale agriculture or peat extraction, and raised roads were established as protection against flooding. In the early Middle Ages, settlements arose in a similar way on mounds located on the salt marsh and along the channels. From these settlements, ring dikes were constructed to protect the nearby area and to intensify reclamation. This created the first polders.

In 1134 AD, a strong storm surge scoured an old estuary of the Sincfal again. Thanks in part to the Zwin, Bruges grew into an international port city. The natural silting up of the salt marsh along the Zwin and the later reclamation caused accelerated natural silting up, making it increasingly difficult for ships to reach Bruges. The reduced navigability of the Zwin channel reinforced the development of outer harbors. A new coastal belt with dunes formed over the already silted up part of the Zwin estuary between Knokke and the present Zwin reserve. The final coastline and youngest active dunes for the Zwin formed only after the Zwin channel was almost completely closed. During the Eighty Years' War and the War of the Spanish Succession, the Zwin estuary was part of the front line and lines of forts and earth walls were built on both banks at the level of the later land border. Flooding was also a war tactic. During WWI and WWII, the Zwin again received a military function in the Hollandstellung and Atlantikwall, respectively. The tidal area even expanded again recently with the de-poldering of the Willem-Leopold Polder, to slow down the natural silting and siltation.