Nicaea - Canon 7

Since custom and ancient tradition have prevailed that the Bishop of Ælia should be honored, let him, saving its due dignity to the Metropolis, have the next place of honor.

This canon is referring to what we know as Jerusalem.  The Ancient Epitome explains well what has happened and should be done.

There would seem to be a singular fitness in the Holy City Jerusalem holding a very exalted position among the sees of Christendom, and it may appear astonishing that in the earliest times it was only a suffragan see to the great Church of Caesarea.  It must be remembered, however, that only about seventy years after our Lord’s death the city of Jerusalem was entirely destroyed and ploughed as a field according to the prophet.  As a holy city Jerusalem was a thing of the past for long years, and it is only in the beginning of the second century that we find a strong Christian Church growing up in the rapidly increasing city, called no longer Jerusalem, but Aelia Capitolina.  Possibly by the end of the second century the idea of the holiness of the site began to lend dignity to the occupant of the see.¹

What had once been a prominent Christian church had been disrupted and set aside because of the temple destruction by Titus.  Now rebuilding, the church is restored to a place of equal prominence with the other major centers of the day.

¹ The Seven Ecumenical Councils, Canon 7 (NPNF² 14:17).