Geograph - photograph every grid square

In 1940 a network of defences was hastily built all over Britain to prevent an expected German invasion. The most common of these defences were called “pillboxes”, squat concrete forts that were sited at road junctions, canals and other strategic points.

With the passage of time it is estimated that fewer than 6,000 of a total of 28,000 pillboxes built still survive. They remain as permanent monuments and a silent tribute to the courage and tenacity of the British people during the dark days of 1940 when Britain stood alone against Nazi Germany.

More detail see Link