We build massive mounds of dirt and rock all the time. We also have a widespread history of building massive stone structures all over the world for thousands of years. The pyramids are impressive, but other than the location and structure they are just another big pile of stones that humans like to make.

Yeah but the Colosseum tho. That's some extremely advanced architecture and it's HUGE. The fact that most of it is still standing after centuries of earthquakes (and being used as a quarry for other construction!) really says something.