Archaeology is a branch of anthropology.
Using the concepts of stratigraphy, or layering, archaeologists are able to reconstruct the sequence of events of the past, and assign dates and significance to various events. It is to preserve the context of artifacts that excavations are carefully controlled, and extensive notes taken. Once a site has been excavated, it is destroyed, existing only in the notes taken. Before any excavation, extensive research is conducted about a site and the area around it. This helps archaeologists to plan their approaches to excavation, and may help clarify what questions they want to answer.