When archaeologists do fieldwork, they look for remains, often by digging in the ground. As settlements (places where people lived in groups) change and grow, old buildings get buried. Usually, this is a natural process. A typical student project is to leave an object in a place where there is nothing going on. It will get covered rather quickly, because wind, water and plants will bury it. Sometimes buildings are deliberately buried to make way for new buildings. Ancient Rome, for example, is now up to 40 feet (12 metres) below the present city. This process of natural or man-made burial is why archaeological fieldwork involves digging, and is expensive and takes a long time.