Dutch Water Line

Old Hollandic Waterline New Hollandic Waterline
Netherlands
One of the inundation sluices near Utrecht
Type	Defensive line
Site information
Controlled by	Netherlands
Site history
Built	1629–1815 (Old) 1815–1940 (New)
In use	1629–1940
Materials	Flooded plains, sluices, earth walls, brick, concrete, steel
Battles/wars	Third Anglo-Dutch War

The Hollandic Water Line (Dutch: Hollandsche Waterlinie, modern spelling: Hollandse Waterlinie) was a series of water-based defences conceived by Maurice of Nassau in the early 17th century, and realised by his half brother Frederick Henry. Combined with natural bodies of water, the Water Line could be used to transform Holland almost into an island. In the 20th century, the Line was extended to include Utrecht.

Early in the Eighty Years' War of Independence against Spain, the Dutch realized that flooding low-lying areas formed an excellent defence against enemy troops. This was demonstrated, for example, during the Siege of Leiden in 1574. In the latter half of the war, when the province of Holland had been freed of Spanish troops, Maurice of Nassau planned to defend it with a line of flooded land protected by fortresses that ran from the Zuiderzee (present IJsselmeer) down to the river Waal.

In 1629, Prince Frederick Henry started the execution of the plan. Sluices were constructed in dikes and forts and fortified towns were created at strategic points along the line with guns covering especially the dikes that traversed the water line. The water level in the flooded areas was carefully maintained at a level deep enough to make an advance on foot precarious and shallow enough to rule out effective use of boats (other than the flat bottomed gun barges used by the Dutch defenders). Under the water level additional obstacles like ditches and trous de loup (and much later, barbed wire and land mines) were hidden. The trees lining the dikes that formed the only roads through the line could be turned into abatis in time of war. In wintertime the water level could be manipulated to weaken ice covering, while the ice itself could be used when broken up to form further obstacles that would expose advancing troops to fire from the defenders for longer.