Primum Mobile
In medieval Christian cosmology, the Primum Mobile ('first mover') or Crystalline Heaven is the outermost sphere of Heaven. Medieval astronomers extrapolated from the observed motion of the planets that the Earth was surrounded by concentric rotating spheres, each of which contained a planet. The outermost visible sphere contained the fixed stars, and it was conjectured that outside that was a final invisible sphere, the Primum Mobile, which also rotated. Since it was the furthest moving sphere before the Empyrean, the Primum Mobile was thought to be the source of time.
Since all planetary motion was ascribed to the rotation of vast spheres around a fixed Earth, calculations for the rotation speed of the Primum Mobile resulted in astronomically fast speeds. Dante used this as a literal representation of the power (or energy) provided by close exposure to God's divine love. However, all these theories were eventually rejected when Galileo, Copernicus and others found better explanations for the apparent movement of the heavens.