The Quinisext Council of Constantinople was held in 692 and was called by the Eastern Church to enact new canon laws and tighten up some of the rules of the Church(and all of Christianity). The only problem was that nobody bothered to contact Rome or even ask her opinion in these matters. The various Popes between Sergius to Sisinnius had either boldly rejected,or just plain ignored any new laws from Constantinople,adding to the already tense relations between the sister Churches. Now it was new Pope Constantine’s turn to confront this ongoing argument. Emperor Justinian II had already blinded and cut out the tongue of an Archbishop he didn’t like so I’m sure Constantine gulped hard when he was summoned to Justinian’s court. The Pope was welcomed like a king into Constantinople and the emperor supposedly kissed his feet,but it was all for show. Justinian ordered the Pope to his city,not to impose the rules of the Quinisext Council,but to show the world that the great Bishop of Rome was at his beck and call. Pope Constantine still refused the new rules and went back to Rome in peace,but as soon as he arrived home it was reported that Justinian had been murdered and overthrown. The new emperor,Philippikos Bardanes,believed in monothelistism,the old heresy that Jesus only had one will,a divine one. Argh! This old thing again! This argument ate up all of Rome’s time for nearly 200 years! It was back now and had an army behind it that was now knocking on the Pope’s door. Constantine refused to submit and thankfully his Roman milita was able to repel the invading forces. This new emperor was in turn overthrown by yet another guy,but this guy,Anastasius II,rejected monothelistism(whew),and left the Pope alone for the remainder of his Papacy.
Pope Constantine was the last Pope to visit the Eastern Church in Constantinople until Pope Paul VI made a trip there in the 1960s,when it was now named Istanbul and the population was mostly Muslim. Constant fighting between the Churches and a formal schism around the year 1053 contributed to 1200 years between visits but every Pope since(except John Paul I)has made the trip,both to strengthen ties between west and east and to strengthen relations with those in the Muslim faith.