Before 2013, Mont-Saint-Michel was linked to the mainland with a tidal causeway. It was a path covered at high tide and shown at low tide. This connection changed over the centuries. The coastal flats (the sand) have been polderised to make pastureland. This means Mont-Saint-Michel became closer to the coast. The Couesnon River was canalised. This helped make the flow of water similar every time the tide rises or falls. However, it developed a silting-up of the bay. In 1879, the tidal causeway was changed into a raised, dry causeway. This stopped the tide from cleaning the silt around the mount.