In Ennead II.1 (40) Plotinus is primarily concerned to argue for the everlastingness of the universe, the heavens, and the heavenly bodies as individual substances. Here he must grapple both with the philosophical issue of personal identity through time and with the rich tradition of cosmology which pitted the Platonists against the Aristotelians and Stoics. What results is a historically informed cosmological sketch explaining the constitution of the heavens as well as sublunar and celestial motion. This book contains an extensive introduction aimed at providing the necessary background in Platonic, Aristotelian, and Stoic cosmology, the text itself, and a line-by-line commentary designed to elucidate its philosophical, philological and historical details.