The ancient philosophers Parmenides, Zeno, and Melisus developed a rational model of metaphysics and ontology -- a coherent set of statements about the nature of existence that taken together as truths would lead to a consistent and rational world. Parmenides built on the model of the Pythagoreans (who also sought an accurate model of metaphysics based on the premise that everything is literally made up of numbers and that the governing principle of the world is mathematics) to say that, in order for existence to be coherent and rational, existence must have these characteristics:

There must be one and only thing in existence, and that thing must be spherical in shape so that all points on its outer edge are equidistant from the center. The One Thing, existence, must have always existed and will never cease to exist. The One Thing, existence, does not change. Human experience, and the existence of more than One Thing, are illusions that make no sense.

Zeno offered some concrete mathematical evidence to support Parmenides case (Zeno's famous paradoxes demonstrate human experience must be illusionary because space can be infinitely divided into halves and thus it is impossible ever to reach a destination, since one must traverse all the half-way points and they are infinite), and Melisus offered one major improvement:

Melisus noticed that if there was only One Thing and it was Finite, there would have to be a substance or void in which that thing Existed and that substance or void would be Another Thing. To resolve this problem, Melisus corrected Parmenides by stating that the One Thing must be infinite in both space and time.

However, I have a question for all three of these philosophers and I am sorry to say they are dead and will not answer it, and have I think no defenders left on earth. I thought of this question myself, I would suppose it has been asked of them before, but I am not certain. If all human experience is illusion, what force drives the illusion? If we experience the Illusion, the Illusion must exist, even if all the items in the illusion including ourselves do not exist. And if the Illusion must exist to hide the One Thing from us (and all three agree the One Thing is hidden from our experience), then two things exist: the One Thing, Existence itself and the Second Thing, the Illusion.

This I think might have caught the gentlemens' attention. For if there are two things, there are boundaries, differentiation, the possibility of strife and motion. And if there are these, then the entire premise is less promising.