History is truly the witness of times past, the light of truth, the life of memory, the teacher of life, the messenger of antiquity; whose voice, but the orator's, can entrust her to immortality?
Historia vero testis temporum, lux veritatis, vita memoriae, magistra vitae, nuntia vetustatis, qua voce alia nisi oratoris immortalitati commendatur?
Original text (Latin)
Notes from Wikiquote
Book II, Chapter 9, section 36