[ELI5] how did they create polder in the Netherlands in the reinassance?

Question

i am really surprised on what techniques and materials did they use to actively dry out parts of the ocean, they started in the middle ages and continued for centuries, and now it is almost 25% of their landmass.

In: Engineering

Answer 1

Build a dike around the area you want to dry up. Install a pump (back then usually a windmill) and pump the water out until it’s dry.