 The later Platonists shared an important commitment with orthodox Christianity, viz. to understand and explain the world in its entirety on the assumption of one principle only, not two principles that could be thought to be in opposition or conflict with one another (Gnosticism). Christians and Platonists also agreed on the assumption that the first principle itself cannot be part of the natural world but must be a transcendent entity whose existence is wholly independent of and prior to this world, and upon which the world’s existence wholly depends. But unlike Christian thinkers, the Platonists did not think that the world came to be at one point in its distant history, nor that the world’s first principle would have manufactured it like a craftsman, or spoken it into existence. Rather, the Platonists thought that the first transcendent principle sustained a set of further immaterial principles and forms from which derive the diversity of the natural biosphere and which, through the agency of divine souls and forming principles (logoi—principles that form matter at different times and places in its various ways), unfold themselves in space and time. This view of an interconnected and complex hierarchy of being was beautifully suited to accommodate and support traditional polytheism (a feature spelled out in particular by Iamblichus and Proclus), but it of course also led to a host of difficult questions the Platonists struggled to clarify, drawing in some instances for assistance on many aspects of Aristotle’s and the Stoics’ philosophies of nature: What precisely is the content of the intelligible world? What is the function of soul? How do immanent logoi operate? What is the ontological status and function of matter? etc. But the most fundamental and formidable difficulty was to explain precisely how an absolute unity (the first principle) could give rise to the obvious diversity of the intelligible and perceptible worlds. The answer the Platonists developed (the roots of which they thought reached back to Plato and his immediate successors in the Academy) was to postulate that the two most fundamental intelligible principles produced by the hyper-intelligible One should be the principle of unity and the principle of diversity as such. Already Plato had apparently spoken about the ‘Monad’ and the ‘unrestricted Dyad’; together, these principles not only bring forth an entire realm of mathematical principles and numbers, but also account for any kind of unified individuality and diversity throughout the hierarchy of being. As Plotinus put it in the characteristic manner of his style: “Being, when it awoke, stood in multiplicity as number and offered provision for the beings, as it were, a preliminary sketch of unities that held place for the beings which were to be founded on them” (Enn. VI 6, 10).