Pope Adeodatus is sometimes called Adeodatus II, because another pope, Deodatus, was also referred to Adeodatus I sometimes. It can be difficult to keep them all straight.
Adeodatus was born in Rome, son of Jovinian. As a young man, he joined the order of St. Benedict, referred to as the Black monks, due to the color of their habits. He became a monk of the Roman cloister of St. Erasmus on Caelian Hill. He remained a monk and a priest and was not elevated to the cardinalate. His past work with monks made him appreciate their work; he chose many monks for important offices.
When Adeodatus was elected, permission was quickly granted by the emperor and the new pope was installed April 11, 672. He was already known for his generosity, especially to the poor and pilgrims. Following that view of life, Adeodatus increased the allowance for the clergy. He gave Venice the right to choose their own doge. He arranged repairs on the Church of St. Peter, not the basilica, and the Church of St. Erasmus at the monastery. He recognized the Abbey of St. Martin of Tours as being exempt from episcopal authorities. However, he made it clear that he was not going to get into the arguments and politics of the Monothelite heresy.
While Adeodatus took a breather from politics and heresies, the Muslims renewed their siege against the Byzantine Empire. In 673, the Emperor’s fleet sailed to Egypt in an attempt to destroy the Arab fleet before it could sail into the Aegean. The main fleet was missed as it had already at Rhodes. But the Byzantine navy did win a battle off the coast of Egypt.
The next year, the Arab fleet sailed up Hellespont to land at Thrace and launched a siege against the capital of Constantinople. There was a land blockade. That is when the Christian Syrian engineer, Callinicus, invented “Greek fire”, a naphta-like substance. With it, he defected to the Empire and fitted the fleet with cannons which could fire this.
In 675, the Arab blockade of Constantinople continued, getting more reinforcements from Syria. At this point, the Monothelite Patriarch Constantine, newly appointed, sent a profession of his faith to the pope. Adeodatus read it and found it unacceptable. When news came that he had rejected the patriarch’s document, the pope’s name was taken off all imperial documents. But that was as far as he went in addressing the continuing problem
The following year, Constantinople was still blockaded by the Arabs. Pope Adeodatus, an old man when elected, died of natural causes on June 17. News got into the besieged city, somehow, that the old pope had died and the new pope had been elected. Word was received from Constantinople in only two months that the emperor had given his permission for the new pope to ascend the chair of Peter.
Emperor Constantine IV ultimately defeated the Muslims in 678.