October (Roman month) October (Roman month) October (from Latin "octo", "eight") or mensis October was the eighth of ten months on the oldest Roman calendar. It had 31 days. October followed September (from "septem", "seven") and preceded November ("novem", "nine"). After the calendar reform that resulted in a 12-month year, October became the tenth month, but retained its numerical name, as did the other months from September through December. Some of the observances in October marked the close of the season for military campaigning and farming, which commenced in March ("Martius", "Mars' month"). October was under the guardianship "(tutela)" of Mars. The Romans
Adoption of the Gregorian calendar days to be omitted from the calendar. Philip II of Spain decreed the change from the Julian to the Gregorian calendar, which affected much of Roman Catholic Europe, as Philip was at the time ruler over Spain and Portugal as well as much of Italy. In these territories, as well as in the Polish–Lithuanian Commonwealth (ruled by Anna Jagiellon) and in the Papal States, the new calendar was implemented on the date specified by the bull, with Julian Thursday, 4 October 1582, being followed by Gregorian Friday, 15 October 1582; the Spanish and Portuguese colonies followed somewhat later "de facto"