 Although 12th century atomists were inspired by Plato, Calcidius’ widely circulated commentary did not include the passages detailing Plato’s geometrical atomism: instead, they developed particle theories and attempted to reconcile these with the doctrine of the four elements. An original attempt by Thierry of Chartes to solve the problem of the different motions of the four elements—fire and air tending upward, earth and water tending downward to different degrees—relied on the relative cohesiveness of different elements to explain the different degrees of mobility (Pabst 1991). Elemental intertransformation shows that elements must be composed of atoms of similar substance, but fire atoms, say, are less entangled with one another and thus more mobile than other kinds of atoms. Other classic problems, including puzzles about the different speeds of particles of a rotating wheel, continued to occupy theorists into the early modern period; this problem was called rota Aristotelis or ‘Aristotle’s wheel’ because of its appearance in the pseudo-Aristotelian Mechanica (Palmerino 2001).