The probable source for the subject was a Byzantine botanical text-book, 'Geoponica', in which it is related how Jupiter, wishing to immortalise the infant Hercules (whose mother was the mortal Alcmene), held him to the breasts of the sleeping Juno. The milk which spurted upwards formed the Milky Way, while some fell downwards giving rise to lilies.

Lilies were once present at the base of the painting, until a part of the original canvas was cut off.