Anna Perenna, an elderly goddess who symbolizes the turning of the year. Her name is probably a mutation of the Latin per annum.
Macrobius (Saturnalia 1.12.6) related that offerings were made to her "ut annare perannareque commode liccat" ("that the circle of the year may be completed happily") and that people sacrificed to her both publicly and privately. Ovid in his Fasti provides a vivid description of the revelry and licentiousness of her outdoor festival where tents were pitched or bowers built from branches, where people asked that Anna bestow as many more years to them as they could drink cups of wine at the festival.
Ovid then tells that Anna Perenna was the same Anna who appears in Virgil's Aeneid as Dido's sister and that after Dido's death, Carthage was attacked by the Numidians and Anna was forced to flee. Eventually Anna ended up in ship which happened to be driven by a storm right to Aeneas' settlement of Lavinium. Aeneas invited her to stay, but his wife Lavinia became jealous. Anna, warned in a dream by Dido's spirit, escaped whatever Lavinia was planning by rushing off into the night and falling into the river Numicus and drowning. Aeneas and his folk were able to track Anna part way. Eventually Anna's form appeared to them and Anna explained that she was now a river nymph hidden in the "perennial stream" (amnis perennis) of Numicus and her name was therefore now Anna Perenna. The people immediately celebrated with outdoor revels. Ovid then notes that some equate Anna Perenna with the Moon or with Themis or with Io or with Amaltheia, but he turns to what he claims may be closer to the truth, that during the Plebeian revolt the rebels ran short on food and an old woman of Bovillae named Anna baked cakes and brought them to the rebels every morning. The Plebeians later set up an image to her and worshipped her as a goddess.
Next Ovid relates that soon after old Anna had become a goddess, the god Mars attempted to get Anna to persuade Minerva to yield to him in love. Anna at last pretends that Minerva has agreed and the wedding is on. But when Mars' supposed new wife was brought into his chamber and Mars removed the veil he found to his chagrin that it was not Minerva but old Anna, which is why people tell coarse jokes and sing coarse songs at Anna Perenna's festivities.
"The happy feast of Anna Perenna is held on the Ides, Not far from your banks, Tiber, far flowing river. The people come and drink there, scattered on the grass, And every man reclines there with his girl. Some tolerate the open sky, a few pitch tents, And some make leafy huts out of branches, While others set reeds up, to form rigid pillars, And hang their outspread robes from the reeds. But they're warmed by sun and wine, and pray For as many years as cups, as many as they drink. There you'll find a man who quaffs Nestor's years, A woman who'd age as the Sibyl, in her cups. There they sing whatever they've learnt in the theatres, Beating time to the words with ready hands, And setting the bowl down, dance coarsely, The trim girl leaping about with streaming hair. Homecoming they stagger, a sight for vulgar eyes, And the crowd meeting them call them 'blessed'. I fell in with the procession lately (it seems to me worth Saying): a tipsy old woman dragging a tipsy old man." - Ovid, Fasti III
Huius etiam prima die ignem novum Vestae aris accendebant, ut incipiente anno cura denuo servandi novati ignis inciperet: eodem quoque ingrediente mense tam in regia curiisque atque flaminum domibus laureae veteres novis laureis mutabantur: eodem quoque mense et publice et privatim ad Annam Perennam sacrificatum itur, ut annare perennareque commode liceat. - Macrobius, Saturnalia 1.XII.6
Encyclopaedia Britannica 11th ed. (1911)
Ovid Fasti, trans. A.S. Kline (2004)
Macrobius Saturnalia trans. Ludwig von Jan, Gottfried Bass, Quedlinburg and Leipzig (1852)