I live in Rome and they often say that it’s difficult to build a subway because of all the ruins underground, so i’ve always wondered, how can an ancient city get so deep underground? Where does all the dirt covering them come from? Were they covered on purpose so they could build over them, or is this a natural phenomenon?
You can especially see this in the foro romano where the ruins are so low underground compared to the streets you can walk on
In: Planetary Science
It’s a natural process of erosion and deposition of material over time, really. While depth can be related to age, it also depends a lot on where the ruins are and their surroundings. Something in a valley will likely collect more, or in an area with looser soil. Rome is something like 2000 years old give or take, so even if a small amount of dirt, debris, or biological matter collects each year, and that adds up cumulatively on such a timescale.
Dust from erosion or volcanoes, combined with silt from rivers and decaying plant material build up over centuries to bury cities and monuments in a thick layer of soil. https://youtu.be/EofirRBIh28
Imagine you didn’t dust your house for 2000 years. That’d be a thick later of dust, wouldn’t it?
As from where the dirt comes from… Everywhere. Rocks constantly erode, there’s dust blown over from the Sahara, etc.
Whenever you build a house you buy bricks, mortar, cement, sand, etc. from somewhere outside the city walls. But when a building erodes the material is mostly left in the streets or in the location of the ruin. Whenever someone wants to build something else on the site it is much easier to build on top of what is now a rubble pile then to dig out the pile and bring inn new materials. So you end up with a basement and the floors of a house filled inn with what used to be the ceiling of the first floor, the upper floors and the roof. Then a new building on top of that. You can have multiple of these layers of houses as people have been building Rome on top of Rome for millennia.
In addition to this you have lots of old underground infrastructure from ancient times. There are wells, cesspits, burial chambers, deep basements, secret tunnels, etc. all over the city. This was intentionally built underground and then just left there.
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