system
Given the following post, respond as if you're commenting on Reddit:
human
How do man made structures get naturally buried and forgotten over time?

Often times you hear of long lost buildings or even full cities that get buried underground and forgotten over the years. How does that happen? How does ground level get higher and higher over the years?
gpt
People tend to build near bodies of water, and areas near bodies of water tend to be depositional environments.  Basically you've got two types of environments...your hills and mountains are where dirt erodes _from_.  Your flatlands and floodplains are where dirt erodes _to_.  People tend to build in the latter, so over long timescales, sediment tends to accumulate (often through occasional floods).  

Also, people bring their own dirt.  Before the advent of dumptrucks, nobody was really interested in going through the massive amount of trouble it would be to haul out the rubbish of a knocked over or burned down house.  Or even the rubbish of everyday life.  The debris would get left behind and the next house built on top.  Eventually you wind up with many layers of old junk burying the ruins of old buildings.  This is especially important in ancient cities.