In 626, during the Persian campaign led by the Byzantine Emperor Heraclius, he was consulted regarding a plan proposed by Sergius, the Patriarch of Constantinople, aimed at reconciling the Miaphysites of Egypt with the Church and gaining their support for the empire.
[4] Cyrus embraced this formula after Sergius assured him that Pope Honorius I in Rome had endorsed it[5] and that it did not contradict the teachings of the Church Fathers or the decisions made at the Council of Chalcedon.
Cyrus, once patriarch, made persistent efforts to reconcile the Miaphysites and Chalcedonians by promoting monenergism, which eventually developed into monothelitism—a belief in a single will.
It was condemned at the Lateran Council of 649[5] and soon lost credibility, earning the derogatory name "enôsis hydrobaphès" or "washy union" in Medieval Greek.
[6] Cyrus appointed Chalcedonian bishops to govern every Egyptian city up to Ansena, and Coptic priests were put to death whenever discovered.
Some Copts made an attempt on Cyrus's life, but the plot was uncovered by Eudocianus, the brother of Domentianus, who was a general in the Muslim conquest of Egypt.
Heraclius was furious and sent Cyrus a letter full of insults, calling him an abject coward and a heathen and asking whether 100,000 Romans were a match for 12,000 barbarians.
Heraclius died in February 641, two months before the fall of the Babylon Fortress, and was succeeded by his two sons Constantine III and Heraclonas as co-emperors.
She had Heraclonas give Cyrus express permission to make peace at any price with the Arabs, but also gave him reinforcements and a new general named Constantine to replace John.
When Theodore returned to Alexandria, he dismissed Domentianus as the military commander of the garrison and exiled him from the city, replacing him with Menas, who was a non-Chalcedonian Copt and popular with the army.
Since Theodore and Cyrus' arrival in Egypt was on September 14, 641, the Feast of the Cross, a great procession was organised from their landing place to Alexandria.
Their entire path was covered in carpets, hymns were sung, and a piece of the True Cross which was earlier brought to Egypt by John, Duke of Barcaina, and stored by the monks of Tabenna, was carried with Cyrus and Theodore.
The local populace was not informed of it until an Arab army approached Alexandria to receive the tribute, and the Byzantine generals told the people not to resist.
Realising what had happened, a furious mob attempted to stone Cyrus, but he said to them "I have made this treaty in order to save you and your children" and wept before them, which calmed the riot.
Valentine had attempted a second revolt, which failed, so to prove his loyalty to the Emperor Constans II he struck at anyone who could be in favour of Martina and Pyrrhus.
Thus, wracked with guilt for losing Egypt, unable to reconcile with the Copts and undo his persecution of them, and with his ambitions shattered, Cyrus fell into depression and, after a week-long illness, died on March 21, 642.
[note 6][3][9] Cyrus communicated with Sergius through three letters, known as the "Satisfactio," which have been preserved in the acts of the Roman Synod of the Lateran and the Sixth Ecumenical Council (Mansi, X, 1004; XI, 560, 562, 964).
They also refuted his claim of support from the Church Fathers and explained that while the divine and human natures of Christ are referred to as one because they belong to the same person and work in harmony, they cannot be physically identified, as they have distinct origins.