The history of the Orthodox Church actually begins in the Acts of the Holy Apostles, with the Descent of the Holy Spirit: When the day of Pentecost had come, they were all together in one place. And suddenly a sound came from heaven like the rush of a mighty wind, and it filled all the house where they were sitting. And there appeared to them tongues as of fire, distributed and resting on each one of them. And they were all filled with the Holy Spirit and began to speak in other tongues, as the Spirit gave them utterance (Acts 2:1-4). As the text further tells us, on that same day, after St. Peter had preached to the gathered people, those who received his word were baptized, and there were added that day about three thousand souls (Acts 2:41), thus constituting the first Christian community at Jerusalem.
This first community of Christians, headed by St. James, the Brother of the Lord the first Bishop of the city was later scattered by the persecutions which followed the stoning of the first martyr of the Christian Church, St. Stephen: And on that day a great persecution arose against the church in Jerusalem; and they were all scattered throughout the region of Judea and Samaria, except the Apostles (Acts 8:1).
At the same time, faithful to the Lord's command to go ... and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit (Matt. 28:19), the Apostles went out and preached wherever they went, first to the Jews and then to the Gentiles, so that in a surprisingly short time, Christian communities had sprung up in all the main centers of the Roman world and beyond. Their exploits are recorded in the Acts, as well in the inner tradition of the Orthodox Church.