system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are ancient historical ruins (for example Ancient Roman structures) situated dozens of feet below the current "ground level"?
gpt
They aren't always, but generally the reason is that before the 19th century we didn't really feel this need to preserve our past, so we built on top of ruins. People would abandon a settlement, then when conditions changed and the area could be repopulated they tended to build a new settlement on the same spot (usually because the original inhabitants chose that spot for a reason, like close to water/food). Multiply this cycle by a few thousand years and there's your answer.