Caca or Cacia is the giantess sister of Cacus, the son of Vulcan who stole cattle from Hercules during the course of his western labors.
Caca betrays her brother by telling Hercules where to find the livestock, which he had himself taken from Geryon. As a reward for her devotion to the god, she was raised as a divinity, claim Lactantius and Servius. Since Libera was the sister of Liber and Fauna was the daughter, sister, or wife of Faunus, Michael Lipka cites Cacus/Caca as an example of divine pairings that are distinct by gender but connected by kinship in his conceptual approach to Roman divinity. According to Lipka, these deities evolved to give complementary gender balance within their area of influence, in this example, cattle-raising, rather than coming into being as pairs.
Caca is likely an earlier Roman goddess, despite the lateness of the sole ancient texts that describe her. She reportedly possessed a sacellum (shrine), most likely in Rome, where sacrifices were offered to her via the help of the Vestals, according to Servius. As a result, she has come to be thought of as a kind of “proto-Vesta,” a fire goddess who shares her brother’s Vulcan-inherited ability to breathe fire.
Weird Italy, Guide to Unusual & Amazing Places to see in Italy. Italy’s news in English: Art, History & Facts