In the Julian calendar the three days of the feast were 9, 11, and 13 May. The myth of origin of this ancient festival, according to Ovid, who derives Lemuria from a supposed Remuria was that it had been instituted by Romulus to appease the spirit of Remus.
Ovid notes that at this festival it was the custom to appease or expel the evil spirits by walking barefoot and throwing black beans over the shoulder at night. It was the head of the household who was responsible for getting up at midnight and walking around the house with bare feet throwing out black beans and repeating the incantation, "I send these; with these beans I redeem me and mine (haec ego mitto; his redimo meque meosque fabis.)." nine times. The household would then clash bronze pots while repeating, "Ghosts of my fathers and ancestors, be gone!" nine times.
Because of this annual exorcism of the noxious spirits of the dead, the whole month of May was rendered unlucky for marriages, whence the proverb Mense Maio malae nubent ("They wed ill who wed in May").
On the culminating day of the Lemuralia, May 13 in 609 or 610 (the day being recorded as more significant than the year), Pope Boniface IV consecrated the Pantheon at Rome to the Blessed Virgin and all the martyrs, and the feast of that dedicatio Sanctae Mariae ad Martyres has been celebrated at Rome ever since.
According to cultural historians, this ancient custom was Christianized in the feast of All Saints' Day, established in Rome first on May 13, in order to de-paganize the Roman Lemuria. In the eighth century, as the popular observance of the Lemuria had faded over time, the feast of All Saints was shifted to November 1, coinciding with the similar Celtic propitiation of the spirits at Samhain.