The Dutch Waterline (Dutch: Hollandsche Waterlinie; modern spelling: Hollandse Waterlinie) was a system of water-based defenses planned by Maurice of Nassau in the early 17th century and built by his half brother, Frederick Henry. Using natural water bodies, the Waterline could turn Holland, the area farthest west in the Netherlands, next to the North Sea, almost into an island. In the 19th century, the line was expanded to include Utrecht.

On July 26, 2021, the line was added to the Defence Line of Amsterdam, becoming part of the Dutch Water Defence Lines UNESCO World Heritage Site.

History

During the early years of the Eighty Years' War against Spain, the Dutch discovered that flooding low areas was a strong way to protect against enemy soldiers. This was shown during the Siege of Leiden in 1574. Later in the war, after the province of Holland was free from Spanish forces, Maurice of Nassau planned to defend it using a line of flooded land protected by forts, stretching from the Zuiderzee (now IJsselmeer) to the river Waal.

In 1629, Prince Frederick Henry began carrying out this plan. Sluices were built in dikes, and forts and fortified towns were created at key points along the line. Guns were placed to cover the dikes that crossed the flooded areas. The water level was kept at a depth that made it hard for enemies to walk through but shallow enough to stop enemy boats, except for flat-bottomed gun barges used by Dutch soldiers. Under the water, hidden obstacles like ditches and trous de loup were placed. Trees along the dikes, which were the only roads through the line, could be turned into abatis during wartime. In winter, the water level was adjusted to weaken ice, while broken ice was used as extra obstacles to expose enemy troops to fire.

The Dutch Water Line proved its usefulness less than forty years after it was built during the Franco-Dutch War (1672), when it stopped the armies of Louis XIV from conquering Holland. However, freezing weather nearly made the line useless. In 1794 and 1795, French revolutionary forces overcame the Water Line only because heavy frost had frozen the flooded areas solid.

After Napoleon’s final defeat in 1815 at the Battle of Waterloo, the United Kingdom of the Netherlands was formed. Soon after, King William I decided to modernize the Water Line. The line was partly moved east of Utrecht.

Over the next 100 years, the new Water Line became the main Dutch defense line. It was expanded and updated in the 19th century, with forts containing round gun towers similar to Martello towers. The line was activated but never attacked during the Franco-Prussian War in 1870 and World War I.

At the start of World War II, most of the earth and brick fortifications in the Water Line were too weak to survive a long siege from modern weapons. To fix this, many pillboxes were added. However, the Dutch had chosen a more eastern main defense line, the Grebbe Line, and gave the Water Line a secondary role.

When the Grebbe Line was broken on May 13, the army withdrew to the Water Line. However, modern military tactics could bypass fixed defense lines, as seen with the French Maginot Line. While Dutch forces fought at the Grebbe Line, German airborne troops captured key points like bridges in Moerdijk, Dordrecht, and Rotterdam. When resistance continued, the Germans forced the Dutch to surrender by bombing Rotterdam and threatening to bomb Utrecht and Amsterdam.

From its creation in 1815 until its final modernization in 1940, about 50 billion euros were spent on the New Dutch Water Line.

After World War II, the Dutch government redesigned the Water Line idea to defend against a possible Soviet invasion. This third version was built more to the east along the IJssel (called the IJssel Line) and in Gelderland. If an invasion happened, water from the Rhine and Waal rivers would be redirected into the IJssel, flooding the area. The plan was never tested and was removed by the Dutch government in 1964.

Today, many forts along the Water Line remain mostly intact. There is growing interest in the Water Line for its natural beauty. Bike tours and hiking paths are organized with the line as a theme. Some forts allow visitors to stay overnight, while others have different uses, such as Utrecht University’s botanical garden in Fort Hoofddijk.

Because of the Water Line’s unique history, the Dutch government considered adding it to the UNESCO World Heritage Site list, like the fortresses around Amsterdam. On July 26, 2021, the line was officially added as a UNESCO World Heritage Site.

A 25-year plan was created by artist Agnes Denes. In 2010, one of the forts, Bunker 599, was opened as a public art project. The bunker was cut open, with a walkway added to allow visitors to see inside and through it. The project was a collaboration between RAAAF and Atelier de Lyon.

Constructions

To protect weak areas along the waterline, a series of forts and fortified towns were built. The following list shows the order of these forts and towns from north to south. Forts specifically built to defend a town are listed with the town’s name in parentheses.

• Permanent Battery De Westbatterij (Muiden)
• Castle Muiderslot (Muiden)
• Fortified town of Muiden
• Fortified town of Weesp
• Fort aan de Ossenmarkt (Weesp)
• Fort Uitermeer
• Fort Hinderdam
• Fort Ronduit (Naarden)
• Fortified town of Naarden
• Permanent batteries at the Karnemelksloot (Naarden)
• Fort Uitermeer
• Fort Kijkuit
• Fort Spion
• Fort Nieuwersluis
• Fort bij Tienhoven
• Fort aan de Klop (Utrecht)
• Fort de Gagel (Utrecht)
• Fort op de Ruigenhoeksedijk (Utrecht)
• Fort Blauwkapel (Utrecht)
• Fort op de Voordorpsdijk (Utrecht)
• Fort aan de Biltstraat (Utrecht)
• Fort Hoofddijk (Utrecht)
• Fort bij Rhijnauwen (Utrecht)
• Lunetten, a series of small crescent-shaped forts:
• Fort bij Vechten (Utrecht)
• Fort bij 't Hemeltje
• Fort bij Jutphaas (Nieuwegein)
• Minor fort Werk aan de Waalse Wetering
• Minor fort Werk aan de Korte Uitweg
• Lunet aan de Snel
• Fort Honswijk
• Minor fort Werk aan de Groeneweg
• Fort Everdingen
• Minor fort Werk aan het Spoel
• Fort Pannerden
• Fort Boven Lent
• Minor fort Werk op de spoorweg bij de Diefdijk
• Fort bij Asperen
• Fort bij de Nieuwe Steeg
• Fort bij Vuren
• Fortified town of Gorinchem
• Fortified town of Woudrichem
• Castle Loevestein
• Minor fort Werk aan de Bakkerskil
• Fort Steurgat
• Fort aan de Uppelse Dijk (Fort Altena)
• Fort Giessen

• Plofsluis