https://nl.wikipedia.org/wiki/Fort_Ellewoutsdijk
Translation :
The fort was built in the shape of a hexagon and was completely surrounded by a moat. On the outside, the fortification is 80 meters wide and 110 meters long; the outer walls are 10 meters high. [1] In the wall on the sea side there are 19 rectangular bomb-proof rooms equipped with barrel vaults made of heavy masonry. Two meters of ground cover has been placed on top of the vaults. On top of this there was originally an earthen parapet behind which the cannons were positioned. Before the invention of the towed artillery and the high-explosive grenade , Fort Ellewoutsdijk was bomb-proof. A total of 500 men could be stationed in the fort. [1]
A few years after the fort's construction, the Netherlands and Belgium concluded the Treaty of London in 1839 . Thanks to the neutrality policy , the need for the fort decreased and in 1918 the last cannons were removed from the fort. During the Second World War, the German army put the fort back into use. It then served as a prison and a machine gun bunker was built on the west side of the fortification. What is special is that NSB members were imprisoned there after the war. In 2011, Hugo Wapperom 's novel The Spider Fly was published. It describes the post-war camp for prisoners from the inside through an authentic correspondence from 1946, an exchange of letters between the resistance leader Piet Wapperom and his wife (Hugo's parents), who was imprisoned in the camp.
Current situation
After the Second World War, the fort was used as a storage facility by the Defense Department . In 1981 it was managed by the Vereniging Natuurmonumenten ; he purchased the fort because of its special ecological value. The fortification is still completely intact. The walls are in a reasonable state of repair, although the vaults have suffered a lot from moisture. Thanks to the award of a large subsidy from the Cultural Heritage Agency of the Netherlands and the province of Zeeland , a gift from Dow Benelux and Nuon plus own resources from Natuurmonumenten, the fort could be restored. The renovation was completed in mid-2011.
Interesting history, unknown by me until today. My family toured several earthen forts like this during travels in the Pennsylvania and Northeast US when I was much younger.
I’m going to look for the book.
Ian