Combining the Stoic doctrine of a universe without beginning with the Biblical doctrine of the beginning and the end of the world, he conceived of the visible world as the stages of an eternal cosmic process, affording also an explanation of the diversity of human fortunes, rewards, and punishments.
==The idea of millions of years comes from the Catholic Church, from Origen of Alexandria (185-254 AD)
Wrong:
Origen: ‘After these statements, Celsus, from a secret desire to cast discredit upon the Mosaic account of the creation, which teaches that the world is not yet ten thousand years old, but very much under that, while concealing his wish, intimates his agreement with those who hold that the world is uncreated. For, maintaining that there have been, from all eternity, many conflagrations and many deluges, and that the flood which lately took place in the time of Deucalion is comparatively modern, he clearly demonstrates to those who are able to understand him, that, in his opinion, the world was uncreated. But let this assailant of the Christian faith tell us by what arguments he was compelled to accept the statement that there have been many conflagrations and many cataclysms, and that the flood which occurred in the time of Deucalion, and the conflagration in that of Phaethon, were more recent than any others.’ Contra Celsum (Against Celsus) 1.19, Ante-Nicene Fathers4:404.