he Greek letters Chi and Rho were unmistakeably inscribed together, written as a monogram. According to Prof. Jack Finegan of the Pacific School of Religion, Berkeley, who also studied the inscription, this particular monogram was used frequently in Antioch (44AD) and Rome in the first century and was a well known designation for those who were among the first non-Jewish Christians (Acts 11:26).
http://www.leaderu.com/theology/burialcave.html
Acts 11:25 Then departed Barnabas to Tarsus, for to seek Saul:
26 And when he had found him, he brought him unto Antioch. And it came to pass, that a whole year they assembled themselves with the church, and taught much people. And the disciples were called Christians first in Antioch.
Syriac Orthodox Patriarchate of Antioch and All the East, is an Oriental Orthodox Church with autocephalous patriarchate founded by Saint Peter and Saint Paul in the 1st century, according to its tradition. The Syriac Orthodox Church is part of Oriental Orthodoxy, a distinct communion of churches claiming to continue the patristic and Apostolic Christology before the schism following the Council of Chalcedon in 451.
wikipedia_antioch