Papal Infallibility was not known in the early undivided Church of the first millennium. The councils knew nothing of it, nor did the early Church Fathers. It was a doctrine which was promulgated and championed by the Ultramontanists of post schism Rome. It was rejected by the Latin Catholic councils of Constance and Basel. Finally, it was defined by Pius IX in 1870 at the first Vatican council amongst considerable opposition. It has widened the schism between East and West ever since.
Libellius Hormisdae (519),signed by 2,500 Eastern bishops:
“Because the statement of our Lord Jesus Christ, when He said, ‘Thou art
Peter, and upon this Rock I will found my Church and the gates of hell shall
not prevail against it, etc,’ cannot be set aside; this, which is said, is
proved by the results; for in the Apostolic See religion has always
been preserved without spot …In which (See) is set the perfect and true
solidity of the Christain religion.”
…“In the Apostolic See the Catholic religion has always been kept undefiled
and her holy doctrine proclaimed. Desiring, therefore, not to be in the
least degree separated from the faith and doctrine of that See, we hope that
we may deserve to be in the one communion with you which the Apostolic See
preaches, in which is the entire and true solidity of the Christian religion:
promising also that the names of those who are cut off from the communion of
the Catholic Church, that is, not consentient with the Apostolic See, shall
not be recited during the Sacred Mysteries (i.e., the Mass). This is my
profession, I have subscribed with my own hand, and delivered to you,
Hormisdas, the holy and venerable Pope of the city of Rome.”