Magistra vitae

Magistra vitae is a Latin expression, used by Cicero in his De Oratore as a female personification of history, translated as "mistress of life", or "life's teacher" in a female sense. Often paraphrased as Historia magistra vitae est, it conveys the idea that the study of the past should serve as a lesson to the future, and was an important pillar of classical, medieval and Renaissance historiography.

The complete phrase, with English translation, is:

Cicero, De Oratore, II, 36.