When in the past a settlement was abandonded by the inhabitants, the left much garbage behind like pottery, bones or tools and the remains of their wooden houses. This is what we call a culture layer. If at any other given the village would be inhabited again, the new inhabitants built their houses on top of the old culture layer of the previous village. Thus, the new village was on a higher level then the old one. This procedure is repeated until our times, meaning if you want to reach the older culture layers, you need to dig deep into the earth. It could as well happen, a village was not inhabited again. However, in such a case, the remains of the village would be covered again by rocks, sand or earth (landslide, erosion, wind). Villages on shores of lakes again would often be swallowed by the rising water and remain nowadays at the bottom of the lake.