Leonardo de Piero Dati, La sfera. Wellcome Library MS 230 (mid 15th century), f.8r
Medieval people imagined the earth to be at the still centre of a dynamic cosmos. It was enclosed within multiple transparent spheres, nested closely within one another like the layers of an onion (a popular analogy of the time). The continuous circular motions of the celestial spheres resonated with extraordinary harmonies inaudible to human ears, exerting a powerful influence on the physical world.