The Stenen beer aan Slaperdijk bij Spaarndam is an old military building – a part of the defence line which was constructed over several decades between the late 1800s and early 1900s. The defence line extends for around 135KM, and protects Amsterdam and the surrounding area. The network of canals, pumps, and forts could be used to direct the flow of water during times of peace, and flood strategic areas to make them impassable in the event of an invasion.
