(Canto 2, line 21)
The "empyreal heaven" is the abode of God, variously referred to as the tenth circle of heaven or the highest heaven. The Empyrean is immobile, surrounding nine layers of circling heavens: the Moon heaven, the Mercury heaven, the Venus heaven, the Sun heaven, the Mars heaven, the Jupiter heaven, the Saturn heaven, the heaven of Fixed Stars, and the Crystalline heaven or Primum Mobile. Dante discusses this cosmology at length in Book 2, chapter 3 of his Convivio. Dante's system is a little bit different from the classical Ptolemaic system, where it is assumed that nine heavens circle around the earth, immobile at the centre. Dante seems to view things more theologically.