This has always confused me. People built their houses, forts, and other buildings at ground level. How do multiple feet of dirt end up covering the buildings in the thousands of years between then and now? Wind?
Hi there -- always more to be said here, but some of these older posts might get you started:
https://www.reddit.com/r/AskHistorians/comments/1b2bkg/how_are_some_ruins_so_wellpreserved/
As the excellent posts linked by /u/jschooltiger say, sediments can come from a number of sources, including wind, decomposition of human products, and the numerous alluvial processes that happen in any particular area. But there are also many sites where these processes don't bury the remains. Here's an example of a newly mapped site from sometime in the late bronze age (approx. 1400 - 700 BCE). Another one from the same period is even less buried, although this one may have been cleaned when it was looted. The area where both of these sites are located is in the eastern Eurasian steppes, where the soil has been a highly stable surface for millennia. What this means in practical terms is that artifacts from early hunter-gatherers can be found at nearly the same depth as artifacts from thousands of years later.
So what are the factors influencing whether sites are buried or not? An important one is the stability and wetness of the local climate. Dry, stable climates lack the water to deposit most of the sediment that would accumulate otherwise. But even the driest places see some water, so there must be enough water to sustain small groundcover like grasses. These plants disturb sites less than their larger plant counterparts and also work to stabilize the soil surface against aeolian erosion.
Not all sites are buried by natural erosion though. Sites in many such regions are still covered with dirt, famously the levantine tells. Sites in these areas have been disturbed by human activities like sweeping and the decomposition of manufactured products like bricks.
There's also a lot to be said for selection bias in where we find sites. Many of the best, most impressive sites are indeed buried, but this is often what protects them. There's an excellent case-study in Arizona, at an important site called snaketown. Half of the central ballcourt was excavated by emil haury in the 1930s and the other half preserved in its unexcavated state. The half excavated was never backfilled by Haury's team and today, it's heavily eroded compared to its preserved twin. This satellite photo shows the damage, but it's even worse on the ground. Sites that are not covered by soil are at substantially higher risk for erosion and re-use or looting. Simply put, we're less likely to find sites that aren't covered by dirt because they may not exist anymore.
