background: these were placed in strategic places, the places where an invading army would likely pass. So the idea was that invading army would be attacked by well protected soldiers. They are so strong, they'll probably be here for 10,000 years. Made of super-strong concrete with crushed stone as aggregate and plenty of steel. Might even survive a direct artillery hit but of course the waves would kill everyone inside. The sad part...a decent house might have been built instead of one small bunker.

There's so much steel in there that it is economically feasible for people to destroy them to sell the scrap. A lot of them met their end this way.