Artifacts such as tools are also primary sources. Other tools that historians use are secondary sources. They are written after a historical event by people who did not witness the event. Books and paintings that are based on primary sources and appear after an event are examples of secondary sources. Yet another tool that historians use is oral history. This is made up of all the unwritten verbal accounts of events. Historians depend on oral history when studying cultures that have no written records. Oral histories include the stories, customs, and songs that people in a culture have passed down from generation to generation.