system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come that aerial bombs from WW2 are still found e.g. in Berlin nowadays? Weren't they visible after having been dropped? Why did they build over them?
gpt
Many of them ended up being covered by the rubble from other bombs dropped in the same area. Bombs were often dropped in clusters and by groups of bombers, so overlapping blast debris isn't uncommon. Once they ended up covered by rubble, nobody knew that they were there and they were bulldozed with the rest of the terrain when restoring the cities and ended up buried beneath the new structures.