Natural philosophy lasted then from Thales up to Archelaus. Of this last Socrates was a hearer. But there are also many others putting forward different tenets concerning the Divine and the nature of the universe, whose opinions if we wished to set them all out would take a great mass of books. But it would be best, after having recalled by name those of them who are, so to speak, the chorus-leaders of all who philosophized in later times and who have furnished starting-points for systems, to hasten on to what follows.[83] 9. _About Parmenides._ [Sidenote: p. 26.] For truly Parmenides also supposed the universe to be eternal and ungenerated and spherical in form.[84] Nor did he avoid the common opinion making fire and earth the principles of the universe, the earth as matter, but the fire as cause and creator. [He said that the ordered world would be destroyed, but in what way, he did not say.][85] But he said that the universe was eternal and ungenerated and spherical in form and all over alike, bearing no impress and immoveable and with definite limits. 10. _About Leucippus._ But Leucippus, a companion of Zeno, did not keep to the same opinion (as Parmenides), but says that all things are boundless and ever-moving and that birth and change are unceasing. And he says that fulness and the void are elements. And he says also that the ordered worlds came into being thus: when many bodies were crowded together [Sidenote: p. 27.] and flowed from the ambient[86] into a great void, on coming into contact with one another, those of like fashion and similar form coalesced, and from their intertwining yet others were generated and increased and diminished by a certain necessity. But what that necessity may be he did not define. 11. _About Democritus._