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Christian liturgical year

The early development of the Christian liturgical year coincided with the Roman Empire (east and west), and later the Byzantine Empire, both of which employed a taxation system labeled the Indiction, the years for which began on September 1. This timing may account for the ancient church's establishment of September 1 as the beginning of the liturgical year, despite the official Roman New Year's Day of January 1 in the Julian calendar, because the Indiction was the principal means for counting years in the empires, apart from the reigns of the Emperors. The September 1 date prevailed throughout all of Christendom for many centuries, until subsequent divisions eventually produced revisions in some places.

After the sack of Rome in 410, communications and travel between east and west deteriorated. Liturgical developments in Rome and Constantinople did not always match, although a rigid adherence to form was never mandated in the church. Nevertheless, the principal points of development were maintained between east and west. The Roman and Constantinopolitan liturgical calendars remained compatible even after the East-West Schism in 1054. Separations between the Catholic General Roman Calendar and Eastern Orthodox liturgical calendar grew only over several centuries' time. During those intervening centuries, the Latin Church Catholic ecclesiastic year was moved to the first day of Advent, the Sunday nearest to St. Andrew's Day (November 30). By the time of the Reformation (early 16th century), the Roman Catholic general calendar provided the initial basis for the calendars for the liturgically oriented Protestants, including the Anglican and Lutheran Churches, who inherited this observation of the liturgical new year.

The present-day Eastern Orthodox liturgical calendar is the virtual culmination of the ancient eastern development cycle, though it includes later additions based on subsequent history and lives of saints. It still begins on September 1, proceeding annually into the Nativity of the Theotokos (September 8) and Exaltation of the Cross (September 14) to the celebration of Nativity of Christ (Christmas), through his death and resurrection (Pascha/Easter), to his Ascension and the Dormition of the Theotokos ("falling asleep" of the Virgin Mary, August 15). This last feast is known in the Roman Catholic church as the Assumption. The dating of "September 1" is according to the "new" (revised) Julian calendar or the "old" (standard) Julian calendar, depending on which is used by a particular Orthodox Church. Hence, it may fall on September 1 on the civil calendar, or on September 14 (between 1900 and 2099 inclusive).

The liturgical calendars of the Coptic and Ethiopian Orthodox churches are unrelated to these systems but instead follow the Alexandrian calendar which fixed the wandering ancient Egyptian calendar to the Julian year. Their New Year celebrations on Neyrouz and Enkutatash were fixed; however, at a point in the Sothic cycle close to the Indiction; between the years 1900 and 2100, they fall on September 11 during most years and September 12 in the years preceding a leap year.