Infallibility of the Pope

Honorius, Pope of Rome (Monothelite)
“We confess a single will of our Lord Jesus Christ, because our nature has truly been assumed by his divinity.”

Council of Constantinople (681)
Condemned a letter by Honorius as, “Altogether alien to the Apostolic Doctrines, to the definitions of the Holy Councils, and to all the accepted fathers.” “And with these we define that there shall be expelled from the Holy Church of God and anathematized Honorius who was at one time Pope of Old Rome, because of what we found written by him to Sergius, where he in all respects followed the latter’s view and confirmed his impious doctrines.”

Council of Chalcedon (451), 28th Canon
Constantinople which is New Rome, was granted special privileges along side those of Old Rome, on the grounds that Old Rome had received its position in the Church because it was the Imperial City.

Jaroslav Pelikan
To the East the Pope was chief bishop because he was Orthodox. To the West he was and always would be orthodox because he was the chief bishop.