The Liniewal door de Haarlemmermeerpolder is a part of the Defence Line of Amsterdam – a network of dykes, pumps and fortifications that was constructed in the late 19th century. Work on the Defence Line was nearing completion in 1914 when World War One broke out, and it was found that the Defence Line had lost much of its value. The Defence Line was adapted into a decentralised defence system, and later closed down completely. The remaining forts are now Unesco protected monuments.
