Theodosius III () was Byzantine emperor from 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 (generals) Leo the Isaurian and Artabasdos. Leo declared himself emperor in the summer of 716 and allied himself with the Umayyad Caliphate, the Islamic empire; Theodosius sought aid from the Bulgarians under Khan Tervel (), setting a firm border at Thrace and ceding the Zagoria region to the Bulgarians, as well as stipulating the payment of tribute to them. Leo then marched his troops to Constantinople, seizing the city of Nicomedia, and capturing many officials, including Theodosius' son, also named Theodosius. With his son in captivity, Theodosius took the advice of Patriarch Germanus and the Byzantine Senate, and negotiated with Leo, agreeing to abdicate and recognize Leo as emperor. Leo entered Constantinople and definitively seized power on 25 March 717, allowing Theodosius and his son to retire to a monastery. Exactly when Theodosius died is uncertain, but it may have been on 24 July 754. History Background After the Umayyad Caliphate was repelled at the first Arab siege of Constantinople (674–678), the Arabs and Byzantines experienced a period of peace between each other. Hostilities were resumed by Byzantine Emperor Justinian II (), resulting in a string of Arab victories. As a consequence, the Byzantines lost control over Armenia and the Caucasian principalities, and the Arabs gradually encroached upon the Byzantine borderlands. Annually, generals from the Caliphate would launch raids into Byzantine territory, seizing fortresses and towns. After 712, the defenses of the Byzantine Empire weakened, as Arab raids penetrated deeper into Byzantine Asia Minor, and Byzantine response to these raids became less common; much of the frontier became depopulated, as the inhabitants were either killed, enslaved, or driven away, a result of this was that many frontier forts,