From the early days of the Christian faith, it was known and accepted that there were five main regions of the universal Church. See the information below, taken from https://orthodoxwiki.org/Pentarchy
Pentarchy (From OrthodoxWiki)
The Pentarchy consisted of the five ancient patriarchates of the undivided Church of the first millennium of her history, including the Churches of Rome, Constantinople, Alexandria, Antioch, and Jerusalem. These major centers of early Christianity, founded by the apostles, were looked to by their respective regions as leaders in Church life, and eventually their bishops came to be regarded as the primates of their areas. The members of the Pentarchy all participated in some form in the first eight Ecumenical Councils, from 325 to 880. Their relationship with each other, despite various periods of rivalry and dispute, was generally in terms of fraternal equality and conciliarity. History After the Ascension, the apostles dispersed to preach Christianity to the world. They each founded different patriarchates. Some of the most prominent disciples of Jesus founded the patriarchates that made up the Pentarchy.
As noted above, all (5) cities were appropriate and valid centers of Christianity for nearly 1000 years.