Defence Line of Amsterdam

Amsterdam, Netherlands

The UNESCO World Heritage Site known as the Defence Line of Amsterdam (in Dutch named Stelling van Amsterdam) is a 135 km long ring of fortifications around Amsterdam, consisting of 42 forts located between 10 to 15 kilometers from the centre, and lowlands that can easily be flooded in time of war. The flooding was designed to give a depth of about 30 cm, insufficient for boats to traverse. Any buildings within 1 km of the line had to be made of wood, so that they could be burnt and the obstruction removed.

The Stelling van Amsterdam is of outstanding universal value as it is an exceptional example of an extensive integrated defence system of the modern period that has survived intact and well conserved since it was created in the later 19th century. It is also notable for the unique way in which the Dutch genius for hydraulic engineering has been incorporated into the defences of the nation's capital city. It is an excellent illustration of how the Netherlands defended itself against attack by water. In this country from time immemorial dykes, sluices and canals nave been built to drain the land; temporary flooding of the land forms the basis of the defensive system. This principle was first applied in the 16th century.

The introduction of the new defensive system laid down in the 1874 Vestingwet (law on the use of fortresses) meant that a number of old fortified towns were relieved of their defensive role and so could expand outside their ramparts, which largely dated from the 17th century. Under the terms of the Vestingwet, the Netherlands would be protected by nine defensive systems, most already in existence. This defensive line was almost complete in the mid-19th century, but it was partly superseded by the Stelling. It was based on flooding, using the intricate polder system of the western part of the Netherlands. The decision was taken to build the forts along the main defence line in non-reinforced concrete, an early application of this material. In 1892 the northern end of the Nieuwe Hollandse Waterlinie was transferred to the Stelling, to form the eastern part of the defensive system. Certain modifications were carried out to the forts, in line with current military thinking. In the first phase forts were built at the mouths of the main watercourses leading into Amsterdam: a coastal fort at the mouth of the Noordzeekanaal, near Ijmuiden, and an island fort and two coastal batteries in the IJ east of the city where it joined the former Zuyder Zee.

The standard forts on the Stelling were built in two stages. Between 1897 and 1906, 18 forts were built, and 10 more, built to a modified design, were added between 1908 and 1914. The entire Stelling was manned throughout the First World War, even though the Netherlands was neutral in that conflict. During this period construction work continued, to be completed in 1920. Two years later the government revised its defensive plan and decided to build the Holland Vesting, which included part of the Stelling, made obsolete with the introduction of aircraft into warfare. Part of the flooding was activated when Germany invaded the Netherlands in May 1940, but no fighting took place. The early forts were not abandoned until some time after the end of the Second World War; some structures are still in use by the Ministry of Defence.

The defensive line is roughly circular, on a radius of approximately 15 km from the city centre, and extends over two provinces. The main defence line is some 135 km long and comprises 45 forts, with a number of ancillary works. The soil is largely peat and clay, with sand in places. The sites of the forts are directly linked with the existing infrastructure of roads, waterways, dykes and settlements. The main defence line runs mainly along pre-existing dykes. The specific qualities of the landscape through which the line passes determined the character of the constructions; there are six main zones. The northern sector provides excellent facilities for flooding because of the large polders and reclaimed land, and so the forts here were only added in the final phase. The north-western sector runs over existing dykes, adapted for military use. The flooding capacity of the western sector was limited because of the city of Haarlem outside the Stelling and the higher ground behind the dunes; as a result there is a relatively larger number of forts, that at Spaarndam being the main one. In the south-western sector, covering the Haarlemmermeerpolder (reclaimed in 1848-52), it was necessary to build a complete new defensive line with closely linked forts. The southern and south-eastern defences run through a region of inaccessible peat bog and link with the earlier Nieuwe Hollandse Watelinie System. Finally, the eastern sector, running along the coast of the former Zuyder Zee, was primarily defended by marines operating offshore; however, two batteries and the Pampus Island fort were built to close the entrance to Amsterdam harbour.

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