The Carmentalia was an ancient festival celebrated every year in honour of the nymph Carmenta (or Carmentis).
This festival was celebrated annually on a.d. III Id. Ian. ‡ and a.d. XVIII Kal. Feb. ‡. Little is known except that Carmentis was invoked in it as Postvorta and Antevorta, epithets which had reference to her power of looking back into the past and forward into the future. The festival was chiefly observed by women.
Two dates in Ianuarius
Carmentis is celebrated on two dates of the Roman calendar, each day called Carmentalia. These dates should be considered as two separate festivals, rather than one festival extending over this period, yet it is not clear to us today, any more than it was during the Late Republic, why two such holidays should be in such close proximity in one month. According to legend, Her cultus predated Rome itself. In some accounts She was known as Nicostrate, the mother of Evander, who was fathered by Mercurius. Evander was the legendary founder of Paletum, a village that gave its name to the Palatine Hill. Her sacred grove, therefore, may have originally lay beneath the Palatine Hill as some ascribe it. Indeed, it may be that it was in Her sacred grove beneath the Palatine that Romulus and Remus were said to have been discovered being suckled by a she-wolf, since Carmentis was so closely associated with the care of infants.
It was said that later Numa Pompilius founded a sacred grove for Her beneath the Capitoline Hill. The dedication of two groves to Carmentis is one possible reason why there were two days celebrated as Carmentalia in the month of January. It was proposed by Huschke that the two festival days represented the Latins of Romulus and the Sabines of Titus Tatius, just as there were two companies of Luperci and two companies of Salii. Were that the case we might expect that She once had a sacred grove on the Esquiline Hill, and that Numa's dedication beneath the Capitoline represented a union of the two culti Carmentalis. There was a complex on the Esquiline where such a grove may have once stood. This was the later Temple of Juno Lucina, next to which was a grove for Mefitis, and beneath which was a sacred grove of the Nymphae. (Later we'll look more closely at Carmentis and Nymphae.) The fasti Praeneste suggests that the second date was added by a victorious Roman general who had left the City by the Porta Carmentalis for his campaign against Fidenae. The gate received its name from its proximity to the sacred grove of Carmentis.
Yet another story was told by Ovid, linking the two dates to a protest by the matrons of Rome in 195 BCE. During the fourth century the Roman Senate had granted patrician matrons the privilege of riding in two- wheeled carriages (carpentum) in reward for their contribution in gold to fulfilling a vow to Apollo made by Camillus. The privilege was later to be temporarily revoked during the Second Punic War (215 BCE) along with sumptuary laws that limited the use of colored cloth and gold that women could wear, in order to save on private expenses and war materials (horses) and thus help in the war effort. But the Senate did not at first renew the privileges at war's end. In 195 Tribunes Marcus Fundanius and Lucius Valerius finally called for the repeal of this lex Oppia, but they were opposed by the brothers Marcus and Publius Junius Brutus. Supporters for repealing the lex Oppia, and those who supported its remaining in effect, gathered daily on the Capitoline to argue over the matter. Soon women began to join in the disputes, their numbers increasing daily, even so much as women from the countryside entered into the City to advocate for their rights. The natural place for them to first congregate would have been at the grove of Carmentis. This may be what Ovid indicates by linking the protest to the Carmentalia. Consul Marcius Porcius Cato spoke out against repealing the lex Oppia. The women then resolved to "refuse to renew their ungrateful husbands' stock" until their privileges were restored, Ovid referring to the women resorting to abortion as their means of protest. Livy indicates otherwise. (Livy 34.1-8; Ovid Fasti 1,621-8).
In a later period the Temple of the Bona Dea would become associated with the use of abortive herbs, and Carmentis associated with the use of the same herbs in birthing. In actuality both Carmentis and the Bona Dea were associated with birthing or prevention of pregnancy, and the difference between the Capitoline and Aventine temples may have been one of class distinction. Eventually the matrons of Rome regained their rights and, according to Ovid, the second Carmentalia was then begun in thanks to the Goddess for Her support. Ovid's story is the least likely and most fanciful to account for the two Carmentaliae of January even as it provides another aspect to the story told by Livy.
The notion that there may have earlier been two groves dedicated to Carmentis prior to the known grove beneath the Capitoline is a reasonable speculation, but still would not account for the two festivals. We are left then with the information provided by the Fasti Praeneste, although the inscription is mutilated and uncertain. This source may indicate that while the Carmentalia held on 11 January was dedicated to Carmentis, that of 15 January was intended to honor Janus as guardian of the Porta Carmentalis.
Different aspects of Carmentis related to Janus, and thus it is possible that a festival for Him would include Carmentis in similar fashion as festivals for Ops and Consus. The fact remains that we don't know today why the month of January has two separate festivals for Carmentis.