One more historical object

So to speak, the newly open object of military history. During road works near the railway crossing at the Verevo station, a German WW2 bunker was excavated by the builders. This is a typical German 'Tobruk', built by the invaders for the defense of the railway crossing. Why the hole in the roof of the bunker is not round, but square? Presumably it was converted after the war to install a concrete pillar.