The Head of a Particular Church outside the Roman Empire was known as Catholicos. The term Catholicos means ‘head of the Church’. The authority of Catholicos is below to that of Patriarch.
In the Roman Empire, there were government employees, named Catholicos. In this sense Catholicos was the one who has authority over a particular geographical area. It is from the beginning of the 5th Century onwards that the term Catholicos is used to signify the head of the Church. In the Persian church the term Catholicos was used from 410 AD on wards.
Catholicos has all the privileges and authorities over his Catholicate in the same way that a Patriarch has over his Patriarchate. In the Arabic Canon the following are said about the authority of a Catholicos
Catholicos is the supreme authority in his church and all has to obey him.
He has authority over all metropolitans and episcopoi.
He is a shepherd who teaches the people of God with authority.
He is the one who takes the final decision about the things related to faith and liturgy.
He has authority to add more feast days and also to dispose.
The name of the Catholicos should be remembered in the liturgical ceremonies.
His decisions are final.
He has the authority to convoke the synod, to appoint new bishops, to erect new eparchies, to change the boundaries of the eparchies and also to transfer the episcopoi. He has full authority over monasteries. He is the defender of faith.