Why are ancient buildings, cities and structures usually found buried underground?
In: 62
Survivor bias. The interesting archeological sites are the ones that were protected by a big pile of dirt or sand. The ones that didn’t get buried aren’t around to look at anymore. They were sacked, demolished, renovated, or eroded. Pompei being buried in a volcanic eruption is an extreme example of this.
The earth is constantly experiencing winds and weather that shifts the landscape. Anything that is stable enough to survive will eventually be covered (or worn down to nothing). It’s basically things getting dusty on a massive scale. You leave a book in a basement for 50 years, it’ll be caked. You leave a building outside for 5000 years, same thing
There are a few potential reasons why ancient sites end up buried:
* They’re buried by the surrounding environment. This can be due to things like shifting desert (Amarna in Egypt), centuries of vegetation turning to soil and new vegetation growing on top (Chichen Itza in Mexico), or an abrupt cataclysm burying the city (Pompeii in Italy).
* The site was intentionally buried by humans. This is most common in the cases of tombs and other burial sites. Occasionally, it could be because a site was intentionally razed, making it far less of a challenge for nature to bury it.
* The site got buried by continued habitation. This is most common in the Fertile Crescent, where mud brick was the most common material. As mud brick buildings gradually eroded (or got destroyed in war) and got rebuilt, it gradually raised the elevation of the city over millennia, forming what archaeologists call a [tell](https://en.wikipedia.org/wiki/Tell_(archaeology%29).
For things like Roman ruins buried shallowly, I’ve heard that it’s worms.
They aerate the soil below and then gravity pushes the stone / bricks down very slightly. Repeat over 2000 years and you get burial.
The most important aspect of real estate is location, location, location. Places that people are living are places that other people would want to live. That’s why cities are in the same place for hundreds to thousands of years even if they get destroyed from natural or human means.
Another factor is that people only recently had access to trucks and other heavy equipment to dig out and move debris and dirt. In the past, if you wanted to build new things on a property, you just demolished what was on it, filled the holes with dirt that people didn’t want, and built on top of that. This buries the old structures under the new ones.
Cities also import more material than they export. Building materials are not harvested inside the city so they need to come in from somewhere. Crafters take in more volume of raw material than they generate in product after carving it down. And in general, trash and waste builds up in a city. This helps provide some of the “material” to cover up the old structures and grow a city on top of an older version of itself.
Imagine you drop a coin in your backyard. It sits on the top of the soil and if you come back tomorrow, unless someone has moved it or it’s been very gusty out, it’s likely going to be in approximately the same place and visible above ground. Maybe it’s a little dirtier than when you left it. After a little while, the wind will pick up enough dirt (etc.) to cover your coin, grass may grow around and over it, disappearing it from view. Progressive layers of everyday natural and manmade materials will build up over time and make it seem like your coin is getting deeper underground (when really the surface level is rising). Still, the coin is only going to get so deep underground while you’re still living on the property and maintaining your house and garden.
If you move out and centuries pass, however, and nobody maintains your property, it will eventually start to crumble and new layers of dirt, rubble, and overgrowth will cover your coin. There is now a little hill where your house used to be. Future humans, passing through, see a nice hill by the river you used to live by and think, what a lovely place to live, and conveniently close to the water! They build their homes there for a while, drop more things of their own, and then move on in time and the cycle starts again. The hill gets a little bigger.
Many cities in very strategic locations have many many layers of habitation. These can form visible mounds if people keep building over each other’s remains. The oldest material is usually the lowest, the newest material (the coin you just dropped) is at the top. This can be disturbed however by things like earthquakes and agriculture (e.g. while plowing, you realize fragments of ancient pottery are being brought up to the surface as the earth shifts – you’ve found an archaeological site below!) You may also find newer material below if someone above has dug a large pit for dumping rubbish or dug deep burials, for e.g. But in general, think of a layer cake: the top layer was laid most recently.
One more thing: different environments will result in speedier / different patterns of coverage. Drop a coin on the beach and come back even a couple of hours later and you probably won’t find it without a metal detector!
Have you ever tried to bury something above ground?
Several different things are going on:
1) ancient ruins obviously can’t be found floating in the air above ground level….if the ground erodes _away_ from a ruin it collapses and erodes away too and there’s nothing left to find. Stuff at the surface tends to either erode away or fall to the ground. That basically leaves ruins in the ground as the only remaining option.
2) People like to build in areas where sediment accumulates. People live near water, floods carry sediments and bury things that exist near water. Up on top of mountains and hills, the ground usually erodes away. But that’s often not where people are building.
3) People bury old things by building on them. People would just knock down the old building, level off the area with dirt, and build on top of it. Much easier than hauling away the rubble when you haven’t yet invented the bulldozer and dumptruck. Especially when people built of mud brick, this results in older ruins being buried under newer ones and cities could actually build up into their own hills of layers of mud brick, known as “tels”. Even the steady accumulation of garbage can cause this sort of thing.
Burying things often preserves them. If they weren’t buried they wouldn’t be found, because they wouldn’t be hidden, or they wouldn’t exist because the weather would have destroyed them.
Wind is always blowing dirt around and rain is washing dirt around. As it moves is collects in low spots between buildings or whatever. In some places it will eventually bury the whole place. In other places the buildings won’t be buried. They will just be destroyed by centuries of weather or be bulldozed to make something new.
In addition to the other stuff mentioned in this thread, many cities and towns were just abandoned. For centuries. Sometimes due to plague decimating the population, or war, or the reason for the city’s existence ceasing to be there any more (a bend in a river moves, a sand dune moves and covers the city, a local mine getting depleted, etc.). So people pick up and move and never return.
So the buildings sit there, exposed to the wind, rain, floods, dust, and other weather with no people to sweep off the streets and sidewalks. And that just accumulates over the years.
If one seasonal flood can leave an inch or two of new dirt/mud on an abandoned city, it only takes 10 years for you get a foot of dirt. 60-ish to cover a typical 6 foot high wall. And if you come across a city covered in dirt and mud, you’re less likely to take up residence there. You’re going to search for a city with the modern conveniences you’re looking for. And over the course of a hundred years, or a few hundred, the city slowly gets buried and people tend to forget both that it ever existed, and where.
Latest Answers