Libera is a fertility goddess in ancient Roman religion. Her origins are unknown; she may have been a fertility goddess of archaic or pre-Roman Magna Graecia. Her Latin name is the feminine form of Liber, (free, or in a cult context, The Free One). At some time during Rome's Regal or very early Republican eras, she became a female counterpart of Liber, also known as Liber Pater (The Free Father), Roman god of wine, male fertility, and a guardian of plebeian freedoms.[1] In this form, she enters Roman history as Triadic cult companion to Ceres and Liber in a temple established on the Aventine Hill ca. 493 BC. The location and context of this early cult mark her association with Rome's commoner-citizens, or plebs; she might have been offered cult as part of Liber's festival, Liberalia, or during Cerealia, in which she would have been subordinate to Ceres. Otherwise, her relationship to her Aventine cult partners is uncertain. [2]

With the institution of the ritus graecia cereris (greek rites of Ceres) c.205 BC, Libera was officially identified with Ceres' daughter Proserpina and acquired with her a Romanised form of Greek mystery rite and attendant mythology, based on Greek cults to Demeter and Persephone. In the late Republican era, Cicero describes Liber and Libera as Ceres' children. At around the same time, possibly in the context of popular or religious drama, Hyginus equates her with Greek Ariadne, as bride to Liber's Greek equivalent, Dionysus: therefore her mythographic associations and identity seem far from straightforward.[3] The older and newer forms of her cult and rites, and their diverse associations, persisted well into the late Imperial era. St. Augustine (AD 354 – 430) observes that Libera is concerned with female fertility, as Liber is with male fertility.[4]

From: Wiki
Libera, in her original Roman conception, was probably a goddess who presided over the fertility of women and especially the reception of semen (Spaeth . A representation of the female genitalia was allegedly kept in her temple. She is sometimes referred to as "the female Bacchus", perhaps because of her close association with the similarly named Liber. While not regularly associated with wine, a statue currently held in the British Musem pictures her holding a thyrsus, a spear bound with ivy or bay leaves, in her right hand, and a bunch of grapes in her left hand. She also wears a wreath of ivy on her head. The statue was found in Roma Vecchia, a suburb of Rome. Knight claims that ancient authors frequently used the name in Libera in referring to Bacchus, but this seems to be a confusion created by Libera's similarity in name to Liber (Knight 96.1). A link to an engraving of the Libera statue may be found here. The Columbia Encyclopedia claims that Libera was sometimes associated with Ariadne.

After the foundation of the Aventine Triad, she assimilated the mythology of the Greek Persephone, and was seen as the daughter of Ceres, who had assimilated the mythology of Demeter. A special cult devoted to the mother and daughter cropped up in Rome in the third century BCE. Libera in this aspect was often referred to as Proserpina (Spaeth 11). This cult emphasized the values of fertility and chastity, and were considered the primary virtues women needed to concern themselves with in Roman culture (12). This pair of deities were also propitiated when prodigies occurred (15). In the late imperial period, depicting departed Roman women in the guise of either Ceres, a mature woman, or Proserpina, a young woman, becomes a popular form of funerary statue to adorn tombs. Some scholars believe such a representation indicated that the deceased had been priestesses or at least devoted worshipers of the goddesses. Others merely suggest that the statues are used so that the deceased women could be memorialized in the type of the ideal mother and daughter (30).

The cult of Ceres and Proserpina was presided over by a woman, distinguishing it from the Italic cult of Ceres and the cult of the Aventine Triad (104). Cicero indicates that this woman, called the sacerdos Cereris or sacerdos Cerealis, would be an older woman of noble birth, whose character was considered highly respectable. She was the only woman, aside from the Vestal Virgins, allowed to have a position of power in a public cult. Cicero also indicates that there were certain rites of this cult that men were not admitted to, and that could only be performed by matrons and maidens (106).

From here: Libera
The Liberalia (17 March) is the festival of Liber Pater and his consort Libera. The Romans celebrated Liberalia with sacrifices, processions, ribald and gauche songs, and masks which were hung on trees.

This feast celebrates the maturation of young boys to manhood. Roman boys, usually at age 14, would remove the bulla praetexta, a hollow charm of gold or leather, which parents placed about the necks of children to ward off evil spirits. At the Liberalia ceremony the young men might place the bulla on an altar (with a lock of hair or the stubble of his first shave placed inside) and dedicate it to the Lares, who were gods of the household and family. Mothers often retrieved the discarded bulla praetexta and kept it out of superstition. If the son ever achieved a public triumph, the mother could display the bulla to ward off any evil that might be wished upon the son by envious people. The young men discarded the toga praetexta, which was probably derived from Etruscan dress and was decorated with a broad purple border and worn with the bulla, by boys and girls. The boys donned the clothing of adulthood, the pure white toga virilis, or "man's gown". The garment identified him as a citizen of Rome, making him an eligible voter.

The celebration on March 17 was meant to honor Liber Pater, an ancient god of fertility and wine (like Bacchus, the Roman version of the Greek god, Dionysus). Liber Pater is also a vegetation god, responsible for protecting seed. Liber, again like Dionysius, had female priests although Liber's priests were older women. Wearing wreaths of ivy, the priestesses made special cakes, or libia, of oil and honey which passing devotees would have them sacrifice on their behalf. Over time this feast evolved and included the goddess Libera, Liber Pater's consort, and the feast divided so that Liber governed the male seed and Libera the female. This ancient Italian ceremony was a "country" or rustic ceremony. The processional featured a large phallus which the devotees carried throughout the countryside to bring the blessing of fertility to the land and the people. The procession and the phallus were meant also to protect the crops from evil. At the end of the procession, a virtuous and respected matron placed a wreath upon the phallus.

Related to the celebration of the Liberalia is the Procession of the Argei, celebrated on March 16 and 17. The Argei were 27 sacred shrines created by the Numina (very powerful ancient gods who are divine beings without form or face) and found throughout the regions of Rome. However, modern scholars have not discovered their meaning or use. In the argei celebration, 30 figures also called Argei were fashioned from rushes into shapes resembling men; later in the year they were tossed into the river(s). The origin of this celebration is not certain, but many scholars feel that it may have been a ritualistic offering meant to appease and praise the Numa and that the 30 argei probably represented the thirty elder Roman curiae, or possibly represented the 30 Latin townships. Other ancient scholars wrote that the use of the bull-rush icons was meant to deter celebrants from human sacrifice, which was done to honor Saturn. Some historical documents indicate that the argei (the sacred places) took their names from the chieftains who came with Hercules, the Argive, to Rome and then occupied the Capitoline (Saturnian) Hill. There is no way at present to verify this information, but it does coincide with the belief that Rome was founded by the Pelasgians and the name Argos is linked to that group.

While Liberalia is a relatively unknown event in the modern time, references to Liberalia and the Roman goddess Libera are still found today online and in astrology.

From: Wiki
Also see:
Cerealia
Aventine Hill
Aventine Triad

Ceres {Goddess of the Week}
-- Ceres, Liber and Libera make a triad at Aventine. Many of the links/resources for Ceres also shed light on Libera