system
Given the following post, respond as if you're commenting on Reddit:
human
[Wall-E] How do all those trash towers stay up and how were they made in the first place?
gpt
They were made by the fleets of WALL-E units who worked on Project Reclamation before it went to the dogs, and who kept up at it for centuries after it was abandoned, slowly breaking down one by one. They are stacks of compressed trash blocks. 

They stay up because they are very dense and precisely-placed. 

They also fall over quite spectacularly when sufficiently disturbed (such as when EVE's ship lands, or The Axiom)