Roman calendar ancient Greek calendars; and the Gregorian calendar, which refined the Julian system to bring it into still closer alignment with the solar year and is the basis of the current international standard. Roman dates were counted inclusively forward to the next of three principal days: the first of the month (the kalends), a day less than the middle of the month (the ides), and eight days—nine, counting inclusively—before this (the nones). The original calendar consisted of 10 months beginning in spring with March; winter was left as an unassigned span of days. These months ran for 38 nundinal cycles, each
Adoption of the Gregorian calendar decree expressly limited the reform to lay (i.e. non-religious) matters, as did the Greek decree. None of these reforms affected the dates of religious holidays. (See below.) While the civil administrations of eastern European countries adopted the Gregorian calendar in the 1910s or early 1920s, none of the national Eastern Orthodox Churches have recognised the Gregorian calendar for church or religious purposes. Instead, a Revised Julian calendar was proposed in May 1923 at the . It uses a different leap year rule, modifying a proposal of 1785 in such a way as to maximise the time before its dates start