Commentary Purg XXVIII 139-141

When they were inspired on their holy mountain, Parnassus (that is, when they were most inspired by their muses), the classical poets sang of the age of gold (e.g., Ovid in the beginning of the Metamorphoses, Virgil in his fourth Eclogue).  In doing so, they perhaps had some intimation of this place, scene of the true 'golden age,' where mankind was created in innocence and joy.