In the opening of Chapter 3, Lewis describes influences from the classical period on medieval literature and the Medieval Model. Influences like Virgil, Ovid, and the Bible are too obvious, so he skips over them entirely. Instead, he aims to concentrate on sources that are less easily accessible to readers, focusing particularly on sources written before the third century CE.

Lewis begins with Cicero’s Republic, which dates from approximately 50 BCE. The Republic contains a dream sequence that many medieval writers referenced. It can be found in Chaucer’s Book of the Duchess and Dante’s Paradiso. Other writers also took the idea of a protagonist’s ascent to the celestial sphere from Cicero. The concept of the “celestial sphere” predates Christianity but aligns well with Christian ideas about heaven. Cicero’s works also popularized the prohibition of suicide (referenced in Donne and Spenser), which Cicero in turn took from Plato. Medieval literature owes credit to Cicero for his conception of the Earth as cosmically insignificant in comparison to the entire universe.

Cicero’s ideas often aligned with Christian philosophy, but he primarily espoused pagan philosophies. For example, he described a heaven for statesmen, an idea that runs directly counter to Christian ideas about what heaven is and who it is for.