There's not a lot known about Fortuna Mammosa except Her name and the fact that She had a shrine or altar in that part of Rome called Region XII. This shrine was probably somewhere between the Porta Capena on the Caelian Hill (near the grove of the Camenae) and the Baths of Caracalla in the southern part of the city. The shrine was evidentally old enough or famed enough to be a landmark, as the street by which it was set up was called after it the Vicus Fortunae Mammiosae.

Mammosa, as one might guess, is just what it looks like: it is formed from the Latin root mamma, meaning "breast", with the suffix -ose, which adds the meaning of "abounding in", "full of", or "rich in". Given that, Fortuna Mammosa may either have been famous for having large breasts, or for having many breasts, like the Artemis (Diana) of Ephesus. If the former, perhaps Fortuna Mammosa was a Goddess of abundance and nourishment, who brought good luck in mothering and nurturing, or who helped the milk in a new mother's breasts to flow.

If the latter, She may have been depicted like the Asiatic Nature-Goddess of Ephesus, called Artemis, as She was a Goddess of Nature. She was, however, a distinct Goddess from the Greek Artemis who was assimilated to Her due to some minor similarities; for Artemis of Ephesus was a great goddess of fruitfulness and fertility. She was depicted in an archaic form, Her body tightly sheathed in a decorated skirt, wearing a garlanded breastplate, and with a mural crown on Her head. Her most outstanding feature, however, is that Her torso is completely covered with what have been labelled breasts, a dozen or more; and this had led Her to be called by the ancients Artemis Polymastos ("Artemis Many-breasted"). However, they don't particularly look like breasts and there is some difference of opinion as to just what they are—eggs, dates, and even the testicles of sacrificed bulls have been suggested (I'm with the last one, as that's what they look like the most to me). At any rate, if Fortuna Mammosa resembled this Artemis, She may perhaps be a Goddess of the wild abundance of nature or even the hunt, Who brought the bounty of nature to humans.

That's all conjecture, though.