History is the study and documentation of past events. Historians seek knowledge of the past using ancient artifacts, written documents, oral traditions, art, and environmental markers. History is also an academic field that uses narrative to explain, analyze, question, and examine past events and their causes and impacts. Stories common to a culture but not supported by evidence are usually classified as cultural heritage or legends. History differs from myth in that it is supported by verifiable evidence. Herodotus and Thucydides helped shape the principles of modern historical study.