This unity began to dissolve circa 120ad, again in 150ad, and finally in 180ad.
But I wonder. Is there biblical or extrabiblical evidence of unity with the See of Rome that you might point me to before 150ad?
St. Ignatius, Bishop of Antioch, writing to the church at Rome while travelling to Rome, where he was eaten by lions in the Coliseum(approx. 105 AD):
The Epistle of Ignatius to the Romans
Greeting
Ignatius, who is also called Theophorus, to the Church which has obtained mercy, through the majesty of the Most High Father, and Jesus Christ, His only-begotten Son; the Church which is beloved and enlightened by the will of Him that wills all things which are according to the love of Jesus Christ our God, which also
presides in the place of the region of the Romans, worthy of God, worthy of honour, worthy of the highest happiness, worthy of praise, worthy of obtaining her every desire, worthy of being deemed holy, and which presides over love,
is named from Christ, and from the Father, which I also salute in the name of Jesus Christ, the Son of the Father:
Chapter 3. Pray rather that I may attain to martyrdom
You have never envied any one;
you have taught others. Now I desire that those things may be confirmed which in your instructions you enjoin
http://www.newadvent.org/fathers/0107.htm
Pope Clement, writing in about 95 AD to the Corinthians:
Chapter 1. The Salutation. Praise of the Corinthians Before the Breaking Forth of Schism Among Them.
The church of God which sojourns at
Rome, to the church of God sojourning at
Corinth, to them that are called and sanctified by the
will of
God, through
our Lord Jesus Christ: Grace unto you, and peace, from Almighty God through
Jesus Christ, be multiplied.
Owing, dear brethren, to the sudden and successive calamitous events which have happened to ourselves, we feel that we have been somewhat tardy in turning our attention
to the points respecting which you consulted us;
Chapter 59. Warning Against Disobedience. Prayer.
If, however, any shall disobey the words spoken by Him through us, let them
know that they will involve themselves in transgression and serious danger;
Chapter 63. Hortatory, Letter Sent by Special Messengers.
Right is it, therefore, to approach examples so good and so many, and
submit the neck and
fulfil the part of obedience, in order that, undisturbed by vain sedition, we may attain unto the goal set before us in
truth wholly free from blame. Joy and
gladness will you afford us,
if you become obedient to the words written by us and through the Holy Spirit root out the lawless
wrath of your jealousy according to the intercession which we have made for peace and unity in this letter.
http://www.newadvent.org/fathers/1010.htm