Sergius I was the Ecumenical Patriarch of Constantinople from 610 to 638.

In 626 during the absence of Emperor Heraclius

Heraclius

Heraclius was Byzantine Emperor from 610 to 641.He was responsible for introducing Greek as the empire's official language. His rise to power began in 608, when he and his father, Heraclius the Elder, the exarch of Africa, successfully led a revolt against the unpopular usurper Phocas.Heraclius'...

 on campaign against Sassanid Persia, the Avars

Eurasian Avars

The Eurasian Avars or Ancient Avars were a highly organized nomadic confederacy of mixed origins. They were ruled by a khagan, who was surrounded by a tight-knit entourage of nomad warriors, an organization characteristic of Turko-Mongol groups...

 laid siege

Siege of Constantinople (626)

The Siege of Constantinople in 626 by the Avars, aided by large numbers of allied Slavs and the Sassanid Persians, ended in a strategic victory for the Byzantines...

 to Constantinople

Constantinople

Constantinople was the capital of the Roman, Eastern Roman, Byzantine, Latin, and Ottoman Empires. Throughout most of the Middle Ages, Constantinople was Europe's largest and wealthiest city.-Names:...

. Along with the magister militum

Magister militum

Magister militum was a top-level military command used in the later Roman Empire, dating from the reign of Constantine. Used alone, the term referred to the senior military officer of the Empire...

Bonus

Bonus (patrician)

Bonus was a Byzantine statesman and general, one of the closest associates of Emperor Heraclius , who played a leading role in the successful defense of the imperial capital, Constantinople, during the Avar–Persian siege of 626.-Life:...

, he had been named regent and was in charge of the city's defense. He led a litany

Ektenia

Ektenia , often called simply Litany, is a prayerful petition in the Eastern Orthodox/Eastern Catholic liturgy...

 to Panagia

Panagia

Panagia , also transliterated Panayia or Panaghia, is one of the titles of Mary, the mother of Jesus, used especially in Orthodox Christianity....

 Hodegetria

Hodegetria

A Hodegetria — or Virgin Hodegetria — is an iconographic depiction of the Theotokos holding the Child Jesus at her side while pointing to Him as the source of salvation for mankind...

 just before the final attack of the Avars, and right after completing it a huge storm crushed the invading fleet, saving Constantinople. The storm was credited as a miracle

Miracle

A miracle often denotes an event attributed to divine intervention. Alternatively, it may be an event attributed to a miracle worker, saint, or religious leader. A miracle is sometimes thought of as a perceptible interruption of the laws of nature. Others suggest that a god may work with the laws...

 of the Virgin Mary.

Sergius I promulgated the belief that Jesus Christ had two natures but one will (Monothelitism

Monothelitism

Monothelitism is a particular teaching about how the divine and human relate in the person of Jesus, known as a Christological doctrine, that formally emerged in Armenia and Syria in 629. Specifically, monothelitism teaches that Jesus Christ had two natures but only one will...

). To this end, Sergius sent his archdeacon

Archdeacon

An archdeacon is a senior clergy position in Anglicanism, Syrian Malabar Nasrani, Chaldean Catholic, and some other Christian denominations, above that of most clergy and below a bishop. In the High Middle Ages it was the most senior diocesan position below a bishop in the Roman Catholic Church...

 Peter to a synod in Cyprus in 634, hosted by Archbishop

Archbishop

An archbishop is a bishop of higher rank, but not of higher sacramental order above that of the three orders of deacon, priest , and bishop...

 Arkadios II and with additional representatives from Pope Honorius

Pope Honorius

Pope Honorius could refer to:#Pope Honorius I#*Antipope Honorius II#Pope Honorius II#Pope Honorius III#Pope Honorius IV...

. The anti-Monothelite side in Jerusalem, championed by Maximus the Confessor

Maximus the Confessor

Maximus the Confessor was a Christian monk, theologian, and scholar. In his early life, he was a civil servant, and an aide to the Byzantine Emperor Heraclius...

 and Sophronius, sent to this synod Anastasius Apocrisiarius pupil of Maximus, George of Resh'aina

George of Resh'aina

George of Resh'aina was a 7th century Syriac historian. He was opposed to Maximus the Confessor, the defender of orthodoxy against monotheletism and wrote an unfriendly biography of him. This book also provides a glimpse into the events of his time....

 pupil of Sophronius and two of George's own pupils, and also eight bishops from Palestine. When the two sides were presented to the emperor, the emperor persisted with Monothelitism and so with Sergius.

Monothelitism was declared a heresy

Heresy

Heresy is a controversial or novel change to a system of beliefs, especially a religion, that conflicts with established dogma. It is distinct from apostasy, which is the formal denunciation of one's religion, principles or cause, and blasphemy, which is irreverence toward religion...

 at the Third Council of Constantinople

Third Council of Constantinople

The Third Council of Constantinople, counted as the Sixth Ecumenical Council by the Roman Catholic and Eastern Orthodox churches and other Christian groups, met in 680/681 and condemned monoenergism and monothelitism as heretical and defined Jesus Christ as having two energies and two wills...

(the Sixth Ecumenical Council), AD 680-681.