floralia

Instituted and enshrined (quite literally as there was a state-sponsored temple in which the party was held) during the late Republic and on advice of the Sibyl after a rather devastating drought, the festival dedicated to the goddess Flora commenced on this day with the celebration for the masses—a distinctly plebeian character as opposed to the austere obligations of most patrician holidays—lasting for six days marked by processions and competition, Ludi Floræ, The Games of Flora, her mystery cult, referred to as the Arval Brethren, a priesthood dedicated to the spiritual and superstitious maintenance of agriculture, opened up for a brief period to allow public veneration and revelry.
The time was marked with special theatrical performances, spectacles including circuses and acrobatics, pelting one other with lupins, floral costumes and dressing of wells, and ceremonial hunting of hares and goats, considered salacious creatures and portents of a fertile year. The ancient rites are reflected in customs associated with May Day (see previously here and here).