The Inlaatduiker aan de Zuiderpolder was constructed during the late 19th century. It forms a part of a defence works project which took more than 30 years to build, and spans over 135KM around Amsterdam. It is classed as a monument, and as such is protected by UNESCO. The defence line served – to protect the city in times of war, and was intended to act as a safe retreat for the government and army during any invasions.
