Commentary Purg XXV 130-132

The second exemplar of Chastity is Diana, her story drawn from Ovid (Metam. II.401-530), the tale of the wood nymph Helice (Callisto), who paid for Jupiter's seduction and impregnation of her when, at the request of outraged Juno, Diana banished her from her woodlands.  She was turned into a bear by Juno, and then, by the now more kind Jupiter, into the constellation Ursa Major.