A synaxis (Greek: σύναξις "gathering"; Slavonic: собор, sobor) is a liturgical assembly in Eastern Christianity (the Eastern Orthodox Church and those Eastern Catholic Churches which follow the Byzantine Rite).
In Constantinople, the clergy and faithful would often gather together on specific feast days at a church dedicated to the saint of that day for liturgical celebrations. These gatherings were referred to as synaxes. These synaxes came to have services written specifically for them. A Synaxis often occurs on the day following a Major Feast Day and is in honor of saints who participated in the event. For example, services on the Feast of Theophany (the revelation of the Trinity at the Baptism of Jesus in the Jordan) would be held at Hagia Sophia; then, the next day, a Synaxis was observed in honor of St. John the Forerunner at the church dedicated to him. Over time, the synaxes came into general use and are now celebrated in every church.
Synaxis can also refer to a common commemoration of a number of saints in a single service, such as the Synaxis of the Seventy Apostles. Each individual saint may have his or her own separate feast day, but they are all commemorated together on their synaxis.
Most synaxes are observed as fixed feasts, being celebrated on the same calendar date year after year, though some occur on the nearest Sunday to a particular date. Other synaxes are celebrated on the Paschal cycle, moving backward or forward in the calendar according to the date of Pascha (Easter) that year.
The following are Synaxes which are universally observed in the Rite of Constantinople:
Synaxis of the Theotokos (December 26)
Synaxis of the Seventy Apostles (January 4)
Synaxis of the Forerunner (January 7)
Synaxis of the Holy Fathers of the Sixth Ecumenical Council (January 23)
Synaxis of the Three Great Hierarchs (January 30)
Synaxis of the Archangel Gabriel (March 26 and July 13)
Synaxis of the Holy Fathers of the Second Ecumenical Council (May 22)
Synaxis of the Holy Fathers of the First Ecumenical Council (Sunday before Pentecost)
Synaxis of All Saints (first Sunday after Pentecost)
Synaxis of the Twelve Apostles (June 30)
Synaxis of the Holy Fathers of the Fifth Ecumenical Council (July 25)
Synaxis of the Holy Fathers of the Third Ecumenical Council (September 9)
Synaxis of the Holy Fathers of the Seventh Ecumenical Council (Sunday on or after October 8)