Pillbox. The name, from the shape (often circular in plan and roughly suggesting a ships conning tower) for the German Ferro-concrete small battlefield-redoubts or forts, employed from the autumn of 1917 onwards to defend sections of the line in Flanders. Some of the larger were Quadragular in shape.
It seems that I’m not the only person who finds the pillbox interesting. There is a Pillbox Study Group and copious books on the subject. This photo essay dedicated to British pillboxes from the Second World War is rather good, and this website carries some beautiful images.
Pillboxes are poignant, evocative, deathly places. There is a new one at La Digue du Braek. Like the old house – Maison du pendu loon-plage – which I built last week, I hope that the structure echoes the spirit of this place in real life.