Not to know what happened before you were born is to be a child forever. For what is the time of a man, except it be interwoven with that memory of ancient things of a previous age?
Nescire autem quid ante quam natus sis acciderit, id est semper esse puerum. Quid enim est aetas hominis, nisi ea memoria rerum veterum cum superiorum aetate contexitur? (120)
Original text (Latin)
Notes from Wikiquote
Chapter XXXIV, section 120
Variants
To be ignorant of the past is to be forever a child.