 As we have seen, Iamblichus posited at the top of his system, below the One but above the Intelligible—and thus at a supra-essential level—the dual principles of Limit (peras) and the Unlimited (or Infinite: apeiron). These principles belong to the Pythagorean tradition (see, e.g., Philolaus Fr. 1 Huffman and Nicomachus, Introduction to Arithmetic II, 18, 4), although the main catalysts responsible for their integration into the Neoplatonic system were two indirect accounts, Plato’s Philebus (see above,  Section 3.1)  and Aristotle, Metaphysics Α, 5 (987a15–19): 