The old Roman legend ran as follows: Procas king of Alba left behind him two sons: Numitor, the elder, weak and spiritless, suffered Amulius to wrest the government from him, and reduce him to his father's private property. In the possession of this he lived rich, and, as he desired nothing more, secure: but the usurper dreaded the claims that might be set up by heirs of a different character. He therefore caused Numitor's son to be murdered, and appointed Silvia, his daughter, one of the vestal virgins.

Amulius had no children, or at least only a single daughter; so that the race of Anchises and Aphrodite seemed on the point of expiring, when the love of a god, in opposition to the ordinances of man, gave it perpetuity and a lustre worthy of its origin. Silvia had gone into the sacred grove, to draw pure water from the spring for the service of the temple: the sun quenched its rays; at the sight of a wolf she fled into a cave; there Mars overpowered the timid virgin; and then consoled her with the promise of noble children, as Posidon did Tyro, the daughter of Salmoneus.