You find them scattered throughout Altena: Small concrete buildings with a roof in the shape of a flattened pyramid. They sometimes stand in unexpected places: in the middle of an orchard or an allotment. Others look out lonely over the water. What are these structures and why are they here?
The blocks of concrete are officially called "Group Shelter Type P." From November 1939 to April 1940, they were built by Dutch Defense Forces on the edge of the inundation fields of the Nieuwe Hollandse Waterlinie. They served as a shelter for 12 soldiers, but were ultimately never used for this purpose.
So the group shelters were built by the Dutch. Therefore, they should not officially be called a bunker, because bunkers are German structures. A folktale tells that the materials for them were bought in Germany.
If you take a closer look at the Type P shelters in the Biesbosch Line, you notice 2 things: they often stand on concrete legs and the roofs are covered with hooks.
To begin with the hooks: they were for hanging beams and branches. These were used to hold the earthen cover in place. This cover served as camouflage and additional armor.
The legs were not originally visible. Over the past 80 years, the ground level has dropped in many places due to de-poldering. As a result, the piles have become exposed. You can clearly see from the casemates how far the ground has subsided.
Most of the casemates still stand firmly on their legs. A few, as in Werkendam, have lost their balance.
The New Dutch Waterline runs right through the Biesbosch Line. From Woudrichem to Werkendam, the casemates lie like a chain through the landscape.
Would you like to visit the casemates? On our walking route Rondje Fort Altena (±12,5 km) you will come across several of them. A shorter route is also available at the fort.
Prefer biking? You can too! Cycle from Fort Altena via De Schans to Werkendam, or meander through the polder in a northeasterly direction to Woudrichem. And those with real cycling legs can do both.
Of the total 700 Type P's along the entire waterline, about 550 have survived, several dozen of which are in the Biesbosch Line. If you look around carefully on your wanderings through Altena, that large number is quite extraordinary. You will see that the shelters are sometimes terribly in the way. Nor are they a calling card for "Dutch Design"; they can rightly be called concrete blocks.
One of the reasons so many of the group shelters are still standing is that they were supposed to provide protection from mortars and shells. That would certainly have succeeded had it ever come to that. When attempts were made to demolish them after the war, it proved no easy task. It took many kilos of explosives to collapse the thick walls. Fortunately, because in this way a piece of Dutch history remained intact.
So if you can't beat them, join them, became the motto. Many of the shelters have found alternative uses: from sheep sheds to hibernation sites for bats.
By now, most of the shelters are protected. This is true at least of those between Fort Altena and Woudrichem. They belong to the forts, which are national monuments.
The Koepelkazemat in Werkendam located a stone's throw from Fort Altena is one of the "bunkers" that have found a new use. The original shooting dome was already removed during World War II, but has been replaced by a new dome. From this dome only pictures may be shot: it is a bird-watching shelter!
In addition to a historical and tourist function, the casemates also have an ecological function. Bats soon discovered the bunkers as an ideal hibernation place.
To allow these animals to sleep undisturbed, some of the shelters are equipped with a door with a "mailbox. People can't get in, but the bats can get out. In these Type-Ps, you'll also often find a layer of wet sand on the floor. Bats like moist environments, and the sand helps with that.
In addition, the concrete is also a good substrate for mosses and lichens. Sometimes as many as 15 species of moss grow on 1 bunker!
The Pyramids in the Polder Foundation has photographed and mapped all still existing Type P group shelters. On their website you will find an interactive map that lists all the casemates with historical and technical information. The foundation also expects to release their book "Pyramids in the Polder" during 2020.
On her voyage of discovery through the Biesbosch Line, Lotte visits a number of casemates in addition to a windmill. Experience it with her in episode 1 of 'Lotte discovers the Biesbosch Line'.
Our heartfelt thanks go to Hannie Visser-Kieboom - journalist, guide at Fort Altena and Water Board member - for her information on the group shelters in the region.
Thanks to Eddie Poppe of the Pyramids in the Polder Foundation for permission to use the survey map.