How do historians know what they know about the past?

Evidence, clues, or pieces of the past

Explanation:

They need some way of knowing, so they study evidence,clues, and pieces of the past to figure out history.

Historians look for causes and effects that help to explain how and why events happened. They try to see the past through the eyes of the people who lived it. When they study the past, historians ask themselves questions. For example, historians ask questions such as how societies are similar and different.