The Synaxis of the Glorious and All-Praiseworthy Twelve Apostles of Christ appears to be an ancient Feast. The Church honors each of the Twelve Apostles on separate dates during the year, and has established a general commemoration for all of them on the day after the commemoration of the Glorious and First-Ranked among the Apostles Peter and Paul.
The holy God-crowned Emperor Constantine the Great (May 21) built a church in Constantinople in honor of the Twelve Apostles. There are instructions for celebrating this Feast which date from the fourth century.
For lists of the Apostles’ names, see: Mt.10:2, Mark 3:14, Luke 6:12, Acts 1:13, 26.