Defence Line of Amsterdam
The Defence Line of Amsterdam (Stelling van Amsterdam) is a 135 km long ring of fortifications around Amsterdam made up of forts located 10 to 15 kilometres from the city centre. It was built between 1883 and 1920, and consisted of flooded areas (inundations) and 46 forts. All of this was dedicated to protecting the national stronghold, as an absolute final line of defence for the Kingdom of the Netherlands.
Even during the final stages of its contruction, the invention of the aeroplane and long-range artillery rendered the defence line obsolate. Nevertheless, the forts and the infrastructure were left in place, largely in their original state. The Defence Line of Amsterdam was placed on the UNESCO World Heritage List in 1996.