For example: "[Leucippus and Democritus] argued that the universe consists of nothing but microscopic, indestructible particles moving in a void. The particles don't change: they... maintain a fixed identity forever. But the motion  of the particles within the void will bring about the appearance of change. In this scheme, all matter consists of different rearrangements of the particles, and all change is but the rearrangement of particles. The name the philosophers gave their fundamental particles was atomos..."  "...The indestructible nature of the atoms was crucial: if the atoms could be pulled apart, then they could change, and the philosophers were back where they started, trying to account for how one thing could turn into another. "(Davies p. 86)