Empedocles of Acragas (c. 495 – c. 435 BCE) proposed four archai by which to understand the cosmos: fire, air, water, and earth. Plato (427 – 347 BCE) believed the elements were geometric forms (the platonic solids) and he assigned the cube to the element of earth in his dialogue Timaeus. Aristotle, (384–322 BCE), believed earth was the heaviest element, and his theory of natural place suggested that any earth–laden substances, would fall quickly, straight down, toward the center of the cosmos.