The Synaxis of the Seventy Apostles was established by the Orthodox Church to indicate the equal honor of each of the Seventy. They were sent two by two by the Lord Jesus Christ to go before Him into the cities He would visit (Luke 10:1).
Besides the celebration of the Synaxis of the Holy Disciples, the Church celebrates the memory of each of them during the course of the year:
Saint James the Brother of the Lord (October 23); Mark the Evangelist (April 25); Luke the Evangelist (October 18); Cleopas (October 30), brother of Saint Joseph the Betrothed, and Simeon his son (April 27); Barnabas (June 11); Joses, or Joseph, named Barsabas or Justus (October 30); Thaddeus (August 21); Ananias (October 1); Protomartyr Stephen the Archdeacon (December 27); Philip the Deacon (October 11); Prochorus the Deacon (28 July); Nicanor the Deacon (July 28 and December 28); Timon the Deacon (July 28 and December 30); Parmenas the Deacon (July 28); Timothy (January 22); Titus (August 25); Philemon (November 22 and February 19); Onesimus (February 15); Epaphras and Archippus (November 22 and February 19); Silas, Silvanus, Crescens or Criscus (July 30); Crispus and Epaenetos (July 30); Andronicus (May 17 and July 30); Stachys, Amplias, Urban, Narcissus, Apelles (October 31); Aristobulus (October 31 and March 16); Herodion or Rodion (April 8 and November 10); Agabus, Rufus, Asyncritus, Phlegon (April 8); Hermas (November 5, November 30 and May 31); Patrobas (November 5); Hermes (April 8); Linus, Gaius, Philologus (November 5); Lucius (September 10); Jason (April 28); Sosipater (April 28 and November 10); Olympas or Olympanus (November 10 ); Tertius (October 30 and November 10); Erastos (November 30), Quartus (November 10); Euodius (September 7); Onesiphorus (September 7 and December 8); Clement (November 25); Sosthenes (December 8); Apollos (March 30 and December 8); Tychicus, Epaphroditus (December 8); Carpus (May 26); Quadratus (September 21); Mark (September 27), called John, Zeno (September 27); Aristarchus (April 15 and September 27); Pudens and Trophimus (April 15); Mark nephew of Barnabas, Artemas (October 30); Aquila (July 14); Fortunatus (June 15) and Achaicus (January 4).
With the Descent of the Holy Spirit the Seventy Apostles preached in various lands. Some accompanied the Twelve Apostles, like the holy Evangelists Mark and Luke, or Saint Paul’s companion Timothy, or Prochorus,the disciple of the holy Evangelist John the Theologian, and others. Many of them were thrown into prison for Christ, and many received the crown of martyrdom.
There are two more Apostles of the Seventy: Saint Cephas, to whom the Lord appeared after the Resurrection (1 Cor. 15:5-6), and Simeon, called Niger (Acts 13:1). They also were glorified by apostolic preaching.
There are discrepancies and errors in some lists of the Seventy Apostles. In a list attributed to Saint Dorotheus of Tyre (June 5) some names are repeated (Rodion, or Herodion, Apollos, Tychicus, Aristarchus), while others are omitted (Timothy, Titus, Epaphras, Archippus, Aquila, Olympas). Saint Demetrius of Rostov consulted the Holy Scripture, the traditions passed down by the Fathers, and the accounts of trustworthy historians when he attempted to correct the mistakes and uncertainties in the list in compiling his collection of Lives of the Saints.
The Church in particular venerates and praises the Seventy Apostles because they taught us to honor the Trinity One in Essence and Undivided.
In the ninth century Saint Joseph the Hymnographer composed the Canon for the Synaxis of the Seventy Apostles of Christ.
~Website of the Orthodox Church in America (OCA), https://www.oca.org/saints/lives/2020/01/04/100017-synaxis-of-the-seventy-apostles.