Anna Perenna fell on the Ides of March (March 15) which would have been the first full moon of the year according to the old calendar. It honored the Goddess of the returning year.
Roman men and women would go on picnics in the countryside and prayed that as many more years as cups of wine they could drink at the festival be granted in their lives.
Anna Perenna is the Goddess of the returning year and the calendar cycle. It is said that once when Mars, besotted with love, begged Anna Perenna to intercede for him with Minerva, Anna Perenna agreed and returned with the good news that Minerva had agreed to marry Him. But on the wedding night when the veil was lifted, who was the bride but Anna Perenna herself! (See Ovid Fasti)
Another story, also related by Ovid says that Anna Perenna was first a mortal woman who brought food to the starving rebels during the Plebeian revolt and earned such gratitude that she was deified.
In one story she is a mortal woman who was turned into a nymph by Numicus, a river God. (See Vergil Aeneid)