Note 535 — Chapter VI · LUNAR CALENDARS AND THE WEEK

The old Roman arrangement of the months, though based on the lunar year, is sui generis. Four of the twelve months, viz., March, May, July, and October, had thirty-one days, and the rest twenty-nine days, except February, which had twenty-eight days. All the months thus had an odd number of days, save February, which was specially devoted to purificatory ceremonies and the cult of the dead. This peculiar arrangement appears to have been based on an old belief that odd numbers are of good omen, even numbers, of ill omen (T. Mommsen, Die römische Chronologie bis auf Cæsar, Berlin, 1858, p. 13; Marquardt-Wissowa, Römische Staatsverwaltung, iii,² 284). The superstition, alluded to by Vergil in a famous line—Numero deus impare gaudet (Bucolica, viii, 75)—is supposed to have been derived from Pythagorean speculations regarding the cosmic properties of numbers. It may better be considered a genuinely Italian notion, since like beliefs are found in the folklore of other peoples, notably the old Arabs and the modern Hindus. See I. Goldziher, in Globus, 1901, lxxx, 31; Crooke, Popular Religion and Folk-lore of Northern India,² ii, 51. The choice of 355 days, rather than 354 days, as the length of the Roman lunar year, was undoubtedly determined by the prevalence of the same superstition (Censorinus, De die natali, xx, 4).