rch 15 was the festival of the goddess, Anna Perenna, in ancient Rome
Anna Perenna was an old Roman deity of the circle or "ring" of the year, as the name (per annum) clearly indicates. Her festival fell on the Ides of March (March 15), which would have marked the first full moon in the year in the old lunar Roman calendar when March was reckoned as the first month of the year, and was held at the grove of the goddess at the first milestone on the Via Flaminia. It was much frequented by the city plebs.
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's settlement of Lavinium. Aeneas invited her to stay, but his wife Lavinia became jealous. But 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 pretended that Minerva had agreed and the wedding was on. But when Mars's 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 told coarse jokes and sang coarse songs at Anna Perenna's festivities. Since the festival of Anna Perenna is in the month of Mars, it is reasonable that the Mars and Anna Perenna should be associated, at least in some rites at that time, as cult partners.
Two places of worship of Anna Perenna are attested. One in Buscemi, Sicily, where, in 1899, some inscriptions to Anna and Apollo were found, and in Rome, where a fountain devoted to Anna Perenna rites was unearthened in 1999. Source
"Ovid in Fasti mentions the procession of Anna Perenna on this day, in which a drunken old woman known as the Petreia, is dragged along the streets by a drunken old man, who may represent Mamurius Veturis [see March 14]. Both of these figures seem to represent the old year, much like modern American depictions of Grandfather Time on New Year's Eve.""The Roman goddess of the new year. Her festival was celebrated on March 15. The Romans gave various explanations to the origin or her name, amnis perennis ("eternal stream"): she was a river nymph; her name was derived from annis ("year"); she was a moon-goddess of the running year; also, she was equated with Anna, the sister of Dido, who was received in Latium by Aeneas, but drowned herself in a river. In the class-struggle between the patricians and plebeians she chose the side of the plebeians." Source
Source: School of the Seasons