Tradition
St. Clement of Rome
Recognitions
Book 10 › Chapter 19
Their Destinies
But when he understood from the lessening of her belly that her child was born, he demanded it, that he might devour it; then Rhea presented him with a large stone, and told him that that was what she had brought forth. And he took it, and swallowed it; and the stone, when it was devoured, pushed and drove forth those sons whom he had formerly swallowed. Therefore Orcus, coming forth first, descended, and occupies the lower, that is, the infernal regions. The second, being above him— he whom they call Neptune— is thrust forth upon the waters. The third, who survived by the artifice of his mother Rhea, she put upon a she-goat and sent into heaven.
Source: Recognitions (New Advent)