I am aware that the Celtic Liturgy came from two influences:
Gallican (which came from Ancient Roman influenced by Carthaginan)
Cappadocian (which came from Antioch).
They all were influenced by or came from the Rite of Jerusalem (Liturgy of Saint James).
But the earliest form of the Antiochene Rite is that of the “Apostolic Constitutions” written down in the early fifth century, and from it is derived the Rite of Jerusalem. Until the Council of Chalcedon (451) Jerusalem was in the Antiochene Patriarchate.
Alexandria and Antioch are the starting-points of the two original Eastern rites.