691 AD – Constantine strongly objected to the canons, several of which opposed Roman customs, established by the largely eastern Trullan (or Quinisext) Council assembled under the Eastern Roman Emperor Justinian II.
708 AD – Constantine I was a champion of papal rights against the tyranny of the Byzantine emperors and against the Monothelite heresy, which taught that there was only one will in Christ.
– He was the first to wear the Tiara of Eastern origin. Most likely the lozenge shaped Greek "Epigonation" was adopted at this time. The pope alone among Western bishops wears it.
709 AD – He received as a pilgrim King Cenred of Mercia, who became a monk at Rome.
710 AD – He was flatteringly received by Justinian, who summoned him to Constantinople, probably to obtain his ratification of the Trullan Council.
711 AD – On October 24th, Constantine seems to have done what John VII feared to do, to have approved whatsoever in the canons of this council did not oppose, faith, morals, or the decrees of the Roman Church. Justinian appears to have been satisfied with this.
– After the emperor’s murder, Constantine condemned Justinian’s usurper and successor, Philippicus Bardanes, for being a Monothelite (i.e., follower of the heresy maintaining that Christ had only one will).
713 AD – Constantine was saved from further trouble when the Eastern Roman Emperor Anastasius II deposed Philippicus and restored orthodoxy.
715 AD – Constantine died and was buried in St. Peter’s Basilica Grottoes on April 9th.