Theodosios III or Theodosius III , was Byzantine Emperor from 715 to March 25, 717.

Theodosius was a financial officer and tax collector in the southern portion of the theme

Theme (Byzantine administrative unit)

The themes or themata were the main administrative divisions of the middle Byzantine Empire. They were established in the mid-seventh century in the aftermath of the Muslim conquests of Byzantine territory and replaced the earlier provincial system established by emperors Diocletian and...

 of Opsikion

Opsikion

The Opsician Theme or simply Opsikion was a Byzantine theme located in northwestern Asia Minor . Created from the imperial retinue army, the Opsikion was the largest and most prestigious of the early themes, being located closest to Constantinople...

. According to one theory he was the son of the former Emperor Tiberius III

Tiberios III

Tiberios III was Byzantine emperor from 698 to 21 August 705. Although his rule was considered generally successful, especially in containing the Arab threat to the east, he was overthrown by the former emperor Justinian II and subsequently executed.-Rise to power:Tiberius was a Germanic naval...

. When the thematic troops rebelled against Emperor Anastasius II

Anastasios II (emperor)

Artemius Anastasius , known in English as Anastasios II or Anastasius II, , was Byzantine emperor from 713 to 715....

, he was chosen as emperor. Theodosius did not readily accept this choice and according to the chronicler Theophanes the Confessor

Theophanes the Confessor

Saint Theophanes Confessor was a member of the Byzantine aristocracy, who became a monk and chronicler. He is venerated on March 12 in the Roman Catholic and the Eastern Orthodox Church .-Biography:Theophanes was born in Constantinople of wealthy and noble iconodule parents: Isaac,...

 even attempted to hide in the forests near Adramyttium. Eventually he was found and was acclaimed emperor in May 715.

Theodosius and his troops immediately laid siege 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:...

. Six months later, in November, they gained entry the city. Theodosius showed himself remarkably moderate in his treatment of his predecessor and his supporters. Through the intercession of Patriarch Germanus

Patriarch Germanos I of Constantinople

Saint Germanus I was Patriarch of Constantinople from 715 to 730. He is regarded as a saint, with a feast day of May 12.-Life:According to Theophanes the Confessor, Germanus was a son of patrician Justinian who was executed in 668. Justinian was reportedly involved in the murder of Constans II and...

 I of Constantinople Anastasius II was convinced to abdicate and become a monk in Thessalonica.

Little is known of Theodosius' short reign. He immediately faced an Arab

Arab

Arab people, also known as Arabs , are a panethnicity primarily living in the Arab world, which is located in Western Asia and North Africa. They are identified as such on one or more of genealogical, linguistic, or cultural grounds, with tribal affiliations, and intra-tribal relationships playing...

 invasion deep into Anatolia

Anatolia

Anatolia is a geographic and historical term denoting the westernmost protrusion of Asia, comprising the majority of the Republic of Turkey...

 and the advance of the Arab

Arab

Arab people, also known as Arabs , are a panethnicity primarily living in the Arab world, which is located in Western Asia and North Africa. They are identified as such on one or more of genealogical, linguistic, or cultural grounds, with tribal affiliations, and intra-tribal relationships playing...

 fleet. In 716 he concluded a treaty with Tervel of Bulgaria

Tervel of Bulgaria

Khan Tervel also called Tarvel, or Terval, or Terbelis in some Byzantine sources, was the Emperor of the Bulgarians at the beginning of the 8th century. In 705 he received the title Caesar which was a precedent in history. He was probably a Christian like his grandfather Khan Kubrat...

 favorable to the Bulgaria

Bulgaria

Bulgaria , officially the Republic of Bulgaria , is a parliamentary democracy within a unitary constitutional republic in Southeast Europe. The country borders Romania to the north, Serbia and Macedonia to the west, Greece and Turkey to the south, as well as the Black Sea to the east...

ns in effort to secure support against the Arab invasion. This policy paid off in 719, when they helped relieve the Second Arab siege of Constantinople.

In 717, the strategos

Strategos

Strategos, plural strategoi, is used in Greek to mean "general". In the Hellenistic and Byzantine Empires the term was also used to describe a military governor...

 of the Anatolic Theme

Anatolic Theme

The Anatolic Theme , more properly known as the Theme of the Anatolics was a Byzantine theme in central Asia Minor...

, Leo the Isaurian (the future Leo III

Leo III the Isaurian

Leo III the Isaurian or the Syrian , was Byzantine emperor from 717 until his death in 741...

), rebelled against Theodosius' rule in collusion with Artabasdos

Artabasdos

Artavasdos, Latinized as Artabasdos or Artabasdus , was Byzantine Emperor of Armenian descent from June 741 or 742 until November 743...

, the strategos of the Armeniac Theme

Armeniac Theme

The Armeniac Theme , more properly the Theme of the Armeniacs was a Byzantine theme located in northeastern Asia Minor .-History:...

. Theodosius' son was captured by Leo in Nicomedia, and Theodosius chose to resign the throne on March 25, 717. He and his son subsequently entered the clergy.

By 729 Theodosius is believed to have become bishop of Ephesus

Ephesus

Ephesus was an ancient Greek city, and later a major Roman city, on the west coast of Asia Minor, near present-day Selçuk, Izmir Province, Turkey. It was one of the twelve cities of the Ionian League during the Classical Greek era...

. Modern historians however suspect the bishop was actually his son. Either way, this bishop was last recorded alive on July 24, 754, taking part in the iconoclastic Council of Hieria

Council of Hieria

The iconoclast Council of Hieria was a Christian council which viewed itself as ecumenical, but was later rejected by the Eastern Orthodox and Roman Catholic Churches. It was summoned by the Byzantine Emperor Constantine V in 754 in the palace of Hieria opposite Constantinople. The council...

.

By his unnamed wife, Theodosius III was the father of at least one son, Theodosius (monastic name), perhaps the bishop of Ephesus in 729–after 754.