Theodosius III resigns the throne to the Byzantine Empire to enter the clergy allowing Leo III to take the throne and begin the Isaurian dynasty.

Theodosius III was Byzantine emperor from c. May 715 to 25 March 717. Before rising to power and seizing the throne of the Byzantine Empire, he was a tax collector in Adramyttium. In 715, the Byzantine navy and the troops of the Opsician Theme, one of the Byzantine provinces, revolted against Emperor Anastasius II, acclaiming the reluctant Theodosius as emperor. Theodosius led his troops to Chrysopolis and then Constantinople, the capital, seizing the city in November 715. Anastasius did not surrender until several months later, accepting exile in a monastery in return for safety. Many themes viewed Theodosius to be a puppet of the troops of the Opsician Theme, and his legitimacy was denied by the Anatolics and the Armeniacs under their respective strategoi (generals) Leo the Isaurian and Artabasdos.

The Byzantine Empire, also known as the Eastern Roman Empire, was the continuation of the Roman Empire centred on Constantinople during late antiquity and the Middle Ages. Having survived the events that caused the fall of the Western Roman Empire in the 5th century AD, it endured until the fall of Constantinople to the Ottoman Empire in 1453. The term 'Byzantine Empire' was coined only after its demise; its citizens used the term 'Roman Empire' and called themselves 'Romans'.

Leo III the Isaurian, also known as the Syrian, was the first Byzantine emperor of the Isaurian dynasty from 717 until his death in 741. He put an end to the Twenty Years' Anarchy, a period of great instability in the Byzantine Empire between 695 and 717, marked by the rapid succession of several emperors to the throne, along with ending the continual defeats and territorial losses the Byzantines had suffered during the 7th century. He also successfully defended the Empire against the invading Umayyads and forbade the veneration of icons.