Caca (pronounced KAY-kuh), or Cacia, is a very ancient Roman Goddess of the Hearth, later supplanted by Vesta. She is considered one of the Penates, or the household Gods who watch over the store-room or penus of the house, and whose altar is the central hearth. They bring prosperity and good fortune, and keep the larder well-stocked, and images of Them were kept in a special part of the house called the penetralia, or inner shrine. Vesta Herself was sometimes considered a Penate, likely through Her connection with Caca, and penus was also used of the special storeroom in the Temple of Vesta that housed the sacred relics which, in the legend, were brought by Aeneas out of the ruins of Troy. Like Vesta, Caca was worshipped with a perpetual fire attended by virgins.

According to a myth of Virgil, Caca was the sister of Cacus, a fire-breathing man-eating giant and shepherd who ravaged the countryside around what would be the neighborhood of Rome. Cacus was fond of robbery, and much hated by the locals. Another giant shepherd of great strength named Recaranus (an original Italian God later identified with Hercules) possessed a herd of cattle which one day wandered into the valley of the Circus Maximus. Cacus stole some of them, dragging them off by their tails to confuse anyone trailing him, and shut them up in His cave. Caca, however, loved Recaranus, and told Him what Her brother had done, and where He had hid the cows. Recaranus then recovered his cows, killing Cacus in the process. The locals rejoiced and rewarded Caca for Her betrayal by worshipping Her as a Goddess.

Though Cacus is considered a son of Vulcan, the Roman fire and volcano God, He is also said to be half-human, so Caca may have been thought to be His half-sister and no relation to Vulcan. (Some legends name the Gorgon Medusa as His mother and Vulcan as His father, while still calling him "half-human"; perhaps this is just to introduce some monstrous DNA into the mix.) However, the two clearly are early fire-deities: Their names are said to derive either from caleo, "to be warm, to be hot with passion", or coquo, "to cook, burn, ripen". Some commentators derive Her name from the (rather rude) Latin word cacare, "to defecate or defile" and accordingly make Her a Goddess of vice and excrement; I find this unlikely in view of Her great similarities with Vesta, whose worship placed such a strong emphasis on purity.

The Penates were said to have originated with the Etruscans, who identified four kinds: Jupiter and His retinue, Neptune and His retinue, the Gods of the Upper Worlds, and the Gods of the Lower Worlds. In later times Vesta was considered a Penate, for as every house had its hearth, so every house had its own Vesta. As Caca's worship is earlier than Vesta's, perhaps originally every house had its Caca who watched over and protected the family.

Her shrine in Rome was located on the southwest corner of the Palatine Hill, near to the scalae Caci, or Stairs of Cacus, supposedly near to the cave Her brother had inhabited. It was said to have been founded by Recaranus or Hercules, and there Her sacred fire was kept burning by Her virgin-priestesses.

Alternate spellings: Cacia, Kakia.

Equated with: Vesta