through the building of dikes, drainage canals, and pumping stations. Today, there are more than 3,000 polders throughout the nation. This wasn't enough though, and in 1916, they suffered from severe flooding.
That's when the Dutch decided to work on the Afsluitdijk to protect low-lying areas and the wall off the Zuiderzee from the sea. The seawall was one of the largest engineering feats of its time, spanning 20 mi (32 km) and a final height of 23 ft (7 m) above sea level. More impressive was the fact that it was topped off by sand and clay, and held together by grass.
Read more at:
How the Dutch Built the Netherlands to Protect it from Flooding