 As we would expect from Fragment 1, the world begins with a fitting together. Fragment 1 also indicates that the fitting together should involve a limiter and an unlimited. What is fitted together in Fragment 7 is “the one in the center of the sphere,” which is then called “the hearth.” From the testimony regarding Philolaus’ astronomical system (see 4.2 below) it is clear that what is in the center of Philolaus’ cosmos is the central fire, and surely it is the central fire that is called the hearth in Fragment 7. What are the limiter and the unlimited from which the central fire is put together? Fire is the obvious choice as the unlimited element, and it is limited by being placed at the center of a sphere. Aristotle tells us that the next step was for the nearest part of the unlimited to be drawn in (Metaph. 1091a17), and elsewhere he specifies that it is time, breath and the void, which are drawn in from the unlimited (Arist., Fr. 201). Evidently then Philolaus first envisaged the emergence of a sphere with a fire at its center. As in most Presocratic cosmologies, the cosmos is surrounded by an unlimited expanse, and Philolaus’ central fire draws in time, breath and void from that expanse. Each of these three is itself an unlimited, a continuum not yet limited in any way. Like many other Presocratics Philolaus drew an analogy between the birth of the cosmos and the birth of a human being. At birth the human embryo, which is hot, breathes in cooling air just as the central fire draws in cooling breath from the unlimited. It may be that the interaction of hot fire and cold breath was thought to generate the other prominent stuffs in the world such as earth and water. Void serves to distinguish individual things from each other spatially (Arist., Fr. 201); bits of the central fire were perhaps separated off to form the sun, stars and planets. Time provides the temporal continuum in which the cosmos can develop and according to which the periods of the planets can be measured (see Zhmud 1998 for doubts that time should be included in the cosmology but note that Aristotle refers to time outside the cosmos not only in Fr. 201 but also at De Caelo 279a12, although without specifically mentioning the Pythagoreans). Some have argued that this cosmogony does not distinguish breath and void, since they are drawn in together, and hence that at least this element of the cosmogony is archaic and dates before Philolaus, since it must antedate Anaxagoras, who first made the distinction (Kahn 2001, 37). Breath and void are listed separately, however, along with time as three things drawn in, and there is no obvious reason to assume that the first two are being identified. Moreover, breath and void serve different functions in the cosmogony (cooling and the spatial differentiation of objects), so that it appears more likely that they are not being equated and that Philolaus developed the cosmogony after void and air had been first distinguished by Anaxagoras and Empedocles. Fragment 17 provides us with the only further evidence for Philolaus’ cosmogony, asserting again that the cosmos began to come to be at the middle and adding that it developed symmetrically around the middle. The end of the cosmogony is the astronomical system described in section 4.2 below, in which ten heavenly bodies including the earth encircle the central fire.