The Stelling van Amsterdam (Defence Line of Amsterdam) is a complete ring of fortifications extending more than 135 km around the city of Amsterdam and is the only example of a fortification based on the principle of controlling local water bodies. Built between 1883 and 1920, a ring of 45 forts, along with dikes, sluices and canals, was designed to repel and protect against a land invasion by another European power.
Spread apart in a ring, with distances not exceeding 3.5 km between them, the forts used a combination of firepower and selective flooding for defence. It was all for naught however, as the advent of airpower after the First World War made fortifications like these obsolete. Decommissioned in 1963, the fort network never saw combat service.