 The medieval picture of Pythagoras as a natural philosopher and the medieval understanding of his theory of the nature of the soul were heavily influenced by the Latin commentary on Plato’s Timaeus by Calcidius (4th century CE) and the Commentary on the Dream of Scipio by Macrobius (5th century CE). Calcidius regarded Plato’s Timaeus as a heavily Pythagorean document. Under the influence of the Neopythagorean Numenius, Calcidius assigned to Pythagoras the view that god was unity and matter duality (Hicks 2014, 429). Calcidius describes Plato’s World-Soul in a way that highlights its harmonic structure and Macrobius explicitly ascribes to Pythagoras the view that the soul is a harmony (Commentary on the Dream of Scipio 1.14.19). The doctrine of the harmony of the spheres, which portrays the cosmos as a harmony that is expressed in the music made by the revolutions of the planets, follows from the numerical structure of the World-Soul and was also assigned to Pythagoras by Calcidius. Most medieval Neoplatonic cosmoligies adopted the doctrine, but the reintroduction of Aristotle’s criticism of it in the thirteenth century caused many to abandon the theory until it was revived in the Renaissance by Ficino (Hicks 2014, 434). Later, Shakespeare refers to the doctrine memorably in The Merchant of Venice (V i. 54–65). Cicero’s presentation of it in the Dream of Scipio was also influential in the Renaissance (Heninger 1974, 3).