Afterward the Dutch began an ambitious program of dike and barrier construction called the Delta Works, which lasted more than four decades and cost more than six billion dollars. One crucial project was the eight-kilometer long barrier built to defend Zeeland from the sea. The final component of the Delta Works-a movable barrier protection Rotterdam Harbor and some 1.5 million people-was finished in 1997. Like other primary sea barriers in the strictest standard in the world.