Power Lines

One thing that made me stop and wonder these past weeks is power lines, which is weird, I know, but I have a logical question too. Why did they put power lines above ground? Like we've never done that before with the history I've learned, it's always been underground like aqueducts or the sewer system. When I told my mom this, she said 'my theory is that it has to do with human stupidity, if you hit a power line underground it could kill you, that, or maintenance' or something along those lines, but I really want to know if someone else has any other ideas.