The Defence Line of Amsterdam - A historical perspective

Many defensive works were constructed throughout the centuries to thwart enemy attempts to conquer certain areas. Water traditionally played a major role in the defence of the Netherlands. The Dutch saw the ability to purposely flood vast, uninterrupted polder areas (process called inundation) as an economical and effective way of preventing enemy advance. Obviously, not everything could be flooded, such as intermittent access areas (strips of elevated land and dykes), which were weak areas where the enemy could possibly break through. So fortifications were built at these places. In the 17th and 18th centuries these were mostly earthen ramparts, so-called entrenchments; in times of danger soldiers and artillery were positioned behind them to defend the area concerned. Later, in the 19th century, forts were built in the dry areas above the flood lines.

Inundation was already used for military defence during the Dutch revolt against Spain (Eighty Years’ War, 1568-1648). This method helped liberate towns (Leiden, 1574) and force towns to surrender
('s-Hertogenbosch, 1629). Prince Maurits and later Frederik Hendrik developed a defence plan to protect the country, resulting in the Hollandse Waterlinie (Dutch Inundation Line) in 1672, the year in which France invaded the Netherlands. By inundating all the land from the Zuyder Zee near Muiden, via the River Vecht and past Woerden to beyond Heusden along the River Meuse, the French troops were prevented from conquering the Netherlands. However, more than 120 years later during the severe winter of 1794-1795, when even the large rivers froze over, the French succeeded in their quest. In 1805, when France was in conflict with England and war with Prussia was imminent, work commenced on a defence line around Amsterdam under the command of Cornelius Krayenhoff, a well-known fortification specialist at that time. These ‘Posts of Krayenhoff’ were the forerunners of the current Defence Line of Amsterdam.

Due to increasingly modern, long-range artillery, Krayenhoff's old defence line no longer provided protection after 1860. A new defence line needed to be constructed further away from the capital. The Vestingwet (Fortification Act) of 1874 already included the Defence Line of Amsterdam (still to be constructed) as part of the country's new defence system.