On the Nature of Things (De Rerum Natura)

All things would be jammed; nothing, therefore, could go on, since no other thing would be the first to give way. But in fact, throughout seas and lands and the heights of heaven, we see before our eyes many things move in many ways for various reasons. These things, if there were no void, I need not say would lack and want restless motion; they never would have been begotten at all, since matter jammed on all sides would have been at rest.
346

Again, however solid things are thought to be, you may yet learn from this that they are of rare body: in rocks and caverns the moisture of water oozes through, and all things weep with abundant drops. Food distributes itself through the whole body of living things; trees grow and yield fruit in season because food is diffused through the whole from the very roots over the stem and all the boughs. Voices pass through walls and fly through houses shut; stiffening frost pierces to the bones. Now, if there are no void parts, by what way can the bodies severally pass? You would see it to be quite impossible.
358

Once more, why do we see one thing surpass another in weight though not larger in size? For if there is just as much body in a ball of wool as there is in a lump of lead, it is natural it should weigh the same, since the property of body is to weigh all things downwards.