Ovid’s Metamorphoses, 4.791-803

… Then a chief,
One of their number [of Aithiopian banqueters], asked why she [Medusa] alone
Among her sisters wore that snake-twined hair,
And Perseus answered: ‘What you ask is worth
The telling; listen and I’ll tell the tale.
Her beauty was far-famed, the jealous hope
Of many a suitor, and of all her charms
Her hair was loveliest; so I was told
By one who claimed to have seen her. She, it’s said,
Was violated in Minerva’s shrine
By Ocean’s lord [Neptune]. Jove’s daughter turned away
And covered with her shield her virgin’s eyes,
And then for fitting punishment transformed
The Gorgon’s lovely hair to loathsome snakes.
Minerva still, to strike her foes with dread,
Upon her breastplate wears the snakes she made.’

(Melville, A. D.1986. Ovid Metamorphoses. Oxford University Press).