The Hollandic Water Line is a defense system intended to keep Holland safe from any possible foreign army invasion.
Maurice of Nassau and Frederick Henry realized that the water line could serve as a great defense mechanism way back in the early 17th century. Over the course of the following centuries the line has been extended multiple times and a number of forts have been built around the coast line for further protection of the area. The Dutch found out that they could flood some of the lower areas around the water line for a further defense against attackers. Thus, they would transform Holland into a partial island that would be protected by the water line.
Nowadays some of the forts built on the coast line are serving as tourist attractions. One of them houses the Utrecht University’s botanical garden.