The Carmentalia (January 11 and 15) was the festival of Carmentis, or Carmenta, a prophetic goddess who was the most important of the Camenae. These two days were among the most distinguished festivals of the Roman matrons because Carmentis was considered to be the goddess of childbirth. The traditions which assign a Greek origin to her worship state that her original name was Nicostrate, and that she was the mother of Evander, with whom she came to Italy. After arriving in Latium with her son, she began to prophesy on the Capitoline hill, and was afterwards revered as a deity. Carmentis is also credited with the invention of the Latin alphabet.
The Temple of Carmentis in Rome was situated near the Porta Carmentalis, southeast of the Capitoline. It was entered barefooted because of a prohibition against leather. A flamen Carmentalis and pontifices assisted in her worship. Two Carmentes, called Porrima and Postverta, were worshipped as her sisters and attendants. Ovid (Fasti, 1. 617) describes the second day of the festival on January 15 thus:
When the third sun shall look back on the past Ides, the holy rites will be repeated in honour of the Parrhasian goddess. For of old, Ausonian matrons drove in carriages. Afterwards the honour was taken from them, and every matron vowed not to propagate the line of her ungrateful spouse by giving birth to offspring; and lest she should bear children, she rashly by a secret thrust discharged the growing burden from her womb. They say the senate reprimanded the wives for their daring cruelty, but restored the right of which they had been mulcted; and they ordained that now two festivals be held alike in honour of the Tegean mother to promote the birth of boys and girls. It is not lawful to bring leather into her shrine, lest her pure hearths should be defiled by skins of slaughtered beasts. If you have any love of ancient rites, attend the prayers offered to her; you shall hear names you never heard before, Porrima and Postverta are placated, whether they be thy sisters, Maenalian goddess, or companions. The one is thought to have sung of what was long ago, the other of what should come to pass hereafter.
Pierre Grimal (Dictionary of Classical Mythology) says Carmentis was regarded as a deity of procreation; she was invoked by two names, Prorsa (head first) and Postversa (feet first), the two positions in which a child can be born.