Anna Perenna is the Roman Goddess of long life and renewal, health and plenty. Her two names both make reference to the year: anna means "to live through a year", while perenna means "last many years" (still seen in the English words annual and perennial). She seems to be concerned with cycles of renewal, and connecting the past to the present; She Herself is described in some legends as old, and in others as young. Her festival was held on the Ides of March, the 15th, or midpoint of the month, when in the old calendar the moon was full—and the timing, both within the month as well as within the larger cycle of the year, also points to a relationship with memory, cyclical time, and endings becoming beginnings, for March was considered the first month of the year when springtime was in full flower and newness was all around. According to Macrobius, sacrifices were made to Her with the intent "that the circle of the year may be completed happily". She is likely an original Italian Goddess of health and longevity, and perhaps the calendar as well, as She embodies the concept of the moon-calculated month within the year. Late legends make Her a deified human.
One of these states that Anna Perenna was an old woman from the town of Bollivae in Latium (the area of central Italy that included Rome). Historically, in 494 BCE, the plebeians (the commoners or peasants), tired of paying taxes and being conscripted into the military while having no voice in the government, holed themselves up on the Mons Sacer, or Sacred Mount about three miles northeast of Rome, with intentions to secede. They were finally coaxed back to Rome with the institution of the tribunes, or representatives of the tribes, whose function was to represent the peoples' interests and defend their freedoms against those of the patrician class. In the legend, Anna Perenna brought the plebeians cakes and kept them fed. For these reasons She was always popular with the common people, and after Her death She was considered a Goddess.
In a later legend Anna is a young woman, the sister of Dido, Queen of Carthage. After the death of her sister, Anna fled to Rome, where the hero Aeneas (the cause of Dido's broken heart and subsequent suicide) had settled. Here she ran afoul of his wife Lavinia, and in despair she killed herself by drowning in the River Numicius. Afterwards she was said to have been given the surname Perenna, and worshipped as the nymph of the river. The River Numicius was considered sacred to Anna Perenna; at its source was built a temple to Aeneas as Jupiter Indiges, and at its mouth was the town of Lavinium, said to be named after Lavinia the wife of Aeneas, who is an ancient local Goddess as well. In fact I suspect that Anna Perenna and Lavinia may be aspects of the same Goddess; Lavinia was said to be a prophetess (a common characteristic of water-nymphs), whose father was one Anius, also the eponymous patron of a river, the Anio. The similarities of names (Anius, Anio, Anna) as well as the rivalry over Aeneas do suggest this, as does the fact that to get to the Mons Sacer from Rome one has to cross the Anio.
In yet another tale, She is again an old woman. The God of War, Mars, was in love with Minerva, the Goddess of War and the Arts and a sworn virgin. He asked Anna Perenna to intercide on His behalf; instead She dressed Herself up as Minerva, and, veiled, came to Mars. When He tried to kiss Her She laughed and laughed at Him in scorn. Minerva's main Roman festival, the Quinquatrus, was held just four days after Anna Perenna's and this is usually the explanation given for why they are linked in this legend.
The Festival of Anna Perenna on the 15th of March was beloved by the common people, though it was also an officially recognized holiday. On the evening of the 15th, people would gather at the 1st milestone on the Via Flaminia in Her sacred grove of fruit trees (in bloom at that time of year) by the banks of the Tiber, and camp out, some bringing tents, others making little shelters from leafy tree branches. There they picnicked merrily into the night, feasting, dancing, singing, and celebrating with much wine, toasting to health and long life. It was believed that one would live as many years as the cups of wine one could drink, and so it was of course traditional therefore to get very, very drunk. This festival connected the old and the new; it is interesting to note that the Via Flaminia was famous for its tombs and cemeteries.
Anna Perenna was equated with several Goddesses: Luna, the Roman Moon-Goddess (Her name just means "Moon") as the measurer of time; Themis, the Greek Goddess of Order and a prophetess; the Greek Io, who is also a Moon-Goddess; or with one of the (unnamed) nymphs who nursed the God Zeus.