E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Polydore Virgil says that the Roman youths used to go into the fields and spend the calends of May in dancing and singing in honour of Flora, goddess of fruits and flowers. The early English consecrated May-day to Robin Hood and the Maid Marian, because the favourite outlaw died on that day. Stow says the villagers used to set up May-poles, and spend the day in archery, morris-dancing, and other amusements.
Evil May-day (1517), when the London apprentices rose up against the foreign residents, and did incalculable mischief. The riot lasted till May 22nd.