<Li> EN (endotercissus, an archaic form of intercissus, "halved") on days when most political and religious activities were prohibited in the morning and evening due to sacrifices being prepared or offered but were acceptable for a period in the middle of the day </Li> <P> Each day was also marked by a letter from A to H to indicate its place within the nundinal cycle of market days . </P> <P> The nundinae were the market days which formed a kind of weekend in Rome, Italy, and some other parts of Roman territory . By Roman inclusive counting, they were reckoned as "ninth days" although they actually occurred every eighth day . Because the republican and Julian years were not evenly divisible into eight - day periods, Roman calendars included a column giving every day of the year a nundinal letter from A to H marking its place in the cycle of market days . Each year, the letter used for the markets would shift 2--5 letters along the cycle . As a day when the city swelled with rural plebeians, they were overseen by the aediles and took on an important role in Roman legislation, which was supposed to be announced for three nundinal weeks (between 17 and 24 days) in advance of its coming to a vote . The patricians and their clients sometimes exploited this fact as a kind of filibuster, since the tribunes of the plebs were required to wait another three - week period if their proposals could not receive a vote before dusk on the day they were introduced . Superstitions arose concerning the bad luck that followed a nundinae on the nones of a month or, later, on the first day of January . Intercalation was supposedly used to avoid such coincidences, even after the Julian reform of the calendar . </P> <P> The 7 - day week began to be observed in Italy in the early imperial period, as practitioners and converts to eastern religions introduced Hellenistic and Babylonian astrology, the Jewish Saturday sabbath, and the Christian Lord's Day . The system was originally used for private worship and astrology but had replaced the nundinal week by the time Constantine made Sunday (dies Solis) an official day of rest in AD 321 . The hebdomadal week was also reckoned as a cycle of letters from A to G; these were adapted for Christian use as the dominical letters . </P>

When did we go from 10 months to 12 months