When did the dutch first reclaim land from the sea?

The Dutch first began reclaiming land from the sea in the late Middle Ages, with significant efforts starting in the 12th century. The construction of dikes and the draining of wetlands became more organized in the 14th and 15th centuries, particularly in regions like Friesland and Holland. One of the most notable early projects was the Beemster Polder, reclaimed in 1612. This practice evolved over the centuries, leading to the extensive polder systems seen in the Netherlands today.