Although not a Platonist, strictly speaking, but a Stoic, Posidonius (135-51 B.C.) nevertheless exercised an immense influence on the development of Middle Platonic thought. Among his many works, all unfortunately lost except for a few scant fragments, is a commentary on the Timaeus, which was likely the main source of his influence on Platonism.
Posidonius recognized two principles in the cosmos, one active and one passive: god and matter, respectively. In this he was following Plato's doctrine of the mixing bowl, as put forth in the Timaeus. In his cosmology, Posidonius posited, as did Platonists like Xenocrates and Antiochus, a bipartite cosmos consisting of a supra- and a sub-lunar realm. He considered the supra-lunar realm to be imperishable, and the sub-lunar perishable, dissolving into the void (kenon) outside the cosmos during the conflagration (ekpur
