Once in a while, we hear about construction projects accidently unearthing whole buildings. Cities are built on top of cities. How does that happen? How do cities end up buried beneath the ground to a point where people build new cities on them without realizing they’re even there?
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It’s a kind of selection bias.
All places on the earth are constantly subjected to the forces of erosion (stuff gets carried away by wind or rain) and accumulation (the stuff that gets carried away has to end up somewhere). In most places, these forces don’t balance out exactly; one will usually be stronger than the other.
In places where erosion prevails, anything left unattended will eventually be gone. A good reason not to build your city there in the first place, and if you do, try to take some measures against erosion, turning the city into an accumulation zone (the mere presence of houses acting as a windbreak will already do some of the work). If these measures fail, and people abandon the city, soon nothing will be left for future archeologists to find.
In an accumulation zone, however, the city is constantly being buried under sand, mud, or other debris. Most of it will be removed by the people, but not all. In gardens or on abandoned, overgrown plots, every dying plant adds another small layer of humus. Whenever a house is torn down, the rubble has to go somewhere – why not spread it out evenly over the plot and then build the new house on top? And once the city is abandoned, nature will slowly bury its ruins.
So, whenever we find the remains of ancient cities, it’s exactly *because* they were buried – either by man or by nature. If they weren’t, there would be nothing to find.
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