In Rosemary Rowe's latest mystery novel, A Coin for the Ferryman, Libertus has to solve a murder within two days, before the Lemuralia, the Feast of the Lemures, to avert evil spirits affecting the building of a new roundhouse. (Things are getting worse by the hour, but of course he comes through … review of the book forthcoming)
According to Smith's Dictionary (via LacusCurtius):
LEMURA'LIA or LEMU'RIA, a festival for the souls of the departed, which was celebrated at Rome every year in the month of May. It was said to have been instituted by Romulus to appease the spirit of Remus whom he had slain (Ovid. Fast. V.473, &c.), and to have been called originally Remuria. It was celebrated at night and in silence, and during three alternate days, that is, on the ninth, eleventh, and thirteenth of May. During this season the temples of the gods were closed, and it was thought unlucky for women to marry at this time and during the whole month of May, and those who ventured to marry were believed to die soon after, whence the proverb, mense Maio malae nubent.
Those who celebrated the Lemuralia, walked barefooted, washed their hands three times, and threw nine times black beans behind their backs, believing by this ceremony to secure themselves against the Lemures (Varro, Vita pop. Rom. Fragm. p241, ed. Bipont.; Servius, ad Aen. i.276). As regards the solemnities on each of the three days, we only know that on the second there were games in the circus in honour of Mars (Ovid. Fast. V.597), and that on the third day the images of the thirty Argei, made of rushes, were thrown from the pons sublicius into the Tiber by the Vestal virgins (Ovid. Fast. V.621; Festus, s.v. Depontani; cf. Argei). On the same day there was a festival of the merchants (festum mercatorum, Ovid. Fast. V.670, &c.), probably because on this day the temple of Mercury had been dedicated in the year 495 B.C. (Liv. II.21). On this occasion the merchants offered up incense, and by means of a laurel-branch sprinkled themselves and their goods with water from the well of Mercury at the Porta Capena, hoping thereby to make their business prosper.
11 - Lemuria, Matralia, Orione
12 - Lemuria, dedicaa al tempio di Marte
13 - Lemuria, Quinquatrus a Minerva
14 - Lemuria, Tibernalia, festa di Taurus
15 - Lemuria, Mercuralia, festa di Vesta
Instructions: VII Idus Mai N: LEMURIA Rise and wash before Midnight. Offer beans to the Manes, casting from your mouth over your left shoulder while saying, Haec ego mitto, his redimo meque meosque fabis. Then wash again and bang gongs to drive out the Manes from the house by saying, Manes, exite paterni.
Lemuria is not to be confused with the hypothetical “lost land” variously located in the Indian and Pacific Oceans. ;-)