There's an even bigger point you're missing; there's nothing new under the sun and there never was. Too many people have put too much thought into things and seen far too much for anyone to ever come up with anything truly "new". Whatever culture built these necessarily had predecesors who developed the knowledge and technology to do it. The 4th dynasty Egyptians didn't invent anything that hadn't been around for centuries. If they could have done it thewn there's no reason to believe it couldn't have been done even earlier. If they could do it without science, the wheel, or any technology other than Inclined Plane Technology then an earlier culture should have been able to do it with bronze.