Christians familiar only with the Christian West may be surprised to learn that Ash Wednesday and its customs exist only in the Western church. The Eastern churches have other ways of counting the days of Lent, and of beginning this Great Fast.
The Roman Catholic Church counts Holy Week as part of the Lenten Fast, but not the Sundays during the Lenten season. Therefore, in about the 8th Century, it was necessary to add four days to the beginning of Lent to bring the number of days up to the traditional 40. This was the origin of Ash Wednesday.
The Eastern Christian Churches (both Catholic and Orthodox) consider Great and Holy Week as a separate unit with its own Fasting and Abstinence requirements, not technically included in the Great Lent. Lent liturgically concludes on the evening of the 6th Friday of Great Lent, the vigil of Lazarus Saturday. Although we do not fast (restrict the amount of food eaten) on Saturdays and Sundays, we do continue to abstain from certain kinds of foods on the Weekends of Lent. The Saturdays & Sundays of the Great Fast are counted in the total of days, thus bringing the number up to 40, counted from Clean Monday, the first day of Great Lent.
Great Lent begins for Byzantine Christians with the Vespers of Clean Monday, held on Cheesefare Sunday evening: On Cheesefare Sunday, after Divine Liturgy, we have a great feast with fish, wine, olive oil, eggs and dairy products, which we will eschew for 40 days. (Meat has already been relinquished the Sunday evening before, on Meatfare.) After the meal, we gather in the Church for Forgiveness Vespers, during which the priest begs forgiveness of his flock. The congregation all ask his, and individually, each other’s pardon. In this way, we prepare for the fasting and trials of the Great Lent, Commending ourselves, and one another, and all our lives to Christ our God. No external marking is used (cf. Mt 6:16).
This period is known as The Great Lent or The Great Fast, because there are several Lents (fast periods) in the Byzantine Calendar. The other three major Lents are The Apostles Fast [from All Saints Sunday (the Sunday after Pentecost) until Sts. Peter & Paul (29 June)]; The Fast of the Theotokos [1-14 August]; and The Christmas Lent [15 Nov – 24 Dec]. In addition, there are also several small [one day] fast and abstinence periods. Finally, of course, the beginning of Great Lent depends on the date of Pascha (Easter).
On calendars for most years one sees two dates on which Christians celebrate the resurrection of Christ: Western Easter and Orthodox Pascha. How did this difference occur? In the Apostolic Christian Churches, there is one formula for determining the date of the Feast of the Resurrection: Pascha falls on the first Sunday after the first full moon after the Spring Equinox. At the first Council of Nicæa (AD 325) this calculation was accepted by all churches. We no longer have the actual Acta of the Council, but we know from testimonial evidence that there was also a discussion about the relationship of this Christian Feast of Feasts with the Jewish Passover. This had obviously been a concern from early times: John’s Gospel and the Synoptic Gospels have a slightly different chronology of the events of the Passion.
The Quartodecimans (The Fourteeners) in parts of Syria and Ireland had insisted, even after the Council, that Pascha must be celebrated directly on the day of the Jewish Passover, the 14th day of the Hebrew Month of Nisan. The Irish Church, due to its Eastern origins and Missionaries, celebrated Pascha on that date until the Synod of Whitby in AD 664. To forestall such controversies, the Council of Nicæa had decreed that Pascha could not fall on Passover. Thus far, all the Apostolic Churches agree today. But then the problems start.