The modern study of history is wide-ranging, and includes the study of specific regions and the study of certain topical or thematic elements of historical investigation. However, ancient cultural influences have helped spawn variant interpretations of the nature of history which have evolved over the centuries and continue to change today. History differs from myth in that it is supported by verifiable evidence. Stories common to a particular culture, but not supported by external sources (such as the tales surrounding King Arthur), are usually classified as cultural heritage or legends. Historians also debate the nature of history as an end in itself, as well as its usefulness to give perspective on the problems of the present. Historians often debate which narrative best explains an event, as well as the significance of different causes and effects. History is also an academic discipline which uses narrative to describe, examine, question, and analyze past events, and investigate their patterns of cause and effect. Historians seek knowledge of the past using historical sources such as written documents, oral accounts, art and material artifacts, and ecological markers. "History" is an umbrella term comprising past events as well as the memory, discovery, collection, organization, presentation, and interpretation of these events. Events before the invention of writing systems are considered prehistory. History (from Ancient Greek: ἱστορία, romanized: historíā, lit.'inquiry knowledge acquired by investigation') is the study and the documentation of the past. Those who cannot remember the past are condemned to repeat it.