Leo III the Isaurian (Greek: Λέων ὁ Ἴσαυρος, romanized: Leōn ō Isauros; c. 685 – 18 June 741), 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, along with ending the continual defeats and territorial losses the Byzantines had suffered during the 7th century. He successfully defended the Empire against the invading Umayyads and forbade the veneration of icons.
Leo III was born in Germanikeia (modern Kahramanmaraş in Turkey), within the northern boundaries of Syria, east of Cilicia. His original name was Konon (Greek: Κόνων). Leo III spoke Arabic as his native language, and was described by Theophanes the Confessor as "the Saracen-minded," although there is very little evidence that he was directly influenced by Islam.
Most modern scholars reject the appellation of "the Isaurian" as a misnomer. The nickname first appears in the chronicle of Theophanes the Confessor, written c. 815, as well as in the 8th or 9th-century Parastaseis syntomoi chronikai, but its exact origin is disputed. It may have been a simple textual error, with authors mistaking Leo's hometown as Germanicopolis, Isauria. Alternatively, the term may have been deliberately applied to delegitimize him as "barbaric". Another theory is that it was a nickname originally intended for the earlier Leontius, who also reigned under the name of "Leo". These theories have not been accepted by all scholars; the nickname may as well have been based on his parental background (similar to Leo IV the Khazar, whose nickname was based on his mother's origin).
After the victory of Justinian II, Konon was dispatched on a diplomatic mission to Alania and Lazica to organize an alliance against the Umayyad caliphate under al-Walid I. According to the chronicle written by Theophanes the Confessor, Justinian wanted to get rid of Konon and took back the money that had been given to him to help advance Byzantine interests, thus leaving Konon stranded in Alania. The chronicle describes the mission as successful and Konon returning eventually to Justinian after crossing the Caucasus mountains in May with snowshoes and taking the fortress of Sideron, associated with the Tsebelda fortress, on the way.
Konon was appointed commander (stratēgos) of the Anatolic Theme by Emperor Anastasius II. On his deposition, Konon joined with his colleague Artabasdos, the stratēgos of the Armeniac Theme, in conspiring to overthrow the new Emperor Theodosius III, ostensibly in support of Anastasius. Artabasdos was betrothed to Konon's daughter Anna. In 717, Konon marched on Constantinople, capturing Theodosius' son at Nicomedia. He forced Theodosius to abdicate, promising safety for him and his family. Theodosius then became a monk at Ephesus. On 25 March, abandoning his allegiance to Anastasius, Konon was crowned by Patriarch Germanus I of Constantinople as Emperor Leo III at the Hagia Sophia.
The new emperor was immediately forced to attend to the second Arab siege of Constantinople, which commenced in August of the same year. The Arabs were Umayyad forces sent by Caliph Sulayman ibn Abd al-Malik and serving under his brother Maslama ibn Abd al-Malik. They had taken advantage of the civil discord in the Byzantine Empire to bring a force of 80,000 to 150,000 men and a massive fleet to the Bosphorus, intending to seize the Byzantine capital and destroy the Empire with a single overwhelming attack.
Careful preparations, begun three years earlier under Anastasius II, and the stubborn resistance put up by Leo wore out the invaders. An important factor in the victory of the Byzantines was their use of Greek fire. The Arab forces also fell victim to Bulgarian reinforcements arriving to aid the Byzantines. Leo was allied with the Bulgarians but the chronicler Theophanes the Confessor was uncertain if they were still serving under Tervel of Bulgaria or his eventual successor Kormesiy of Bulgaria.
Faced with the Bulgarian onslaught, the impenetrability of Constantinople's walls, and their own exhausted provisions, the Arabs were forced to abandon the siege in August 718. Sulayman had died the previous year, and his successor Umar II never made a second attempt to capture the city. The siege had lasted 12 months.
Having thus saved the Empire from extinction, Leo proceeded to consolidate its administration, which in the previous years of anarchy had become completely disorganized. In 718 he suppressed a rebellion in Sicily. The following year saw the deposed Emperor Anastasius II raise an army and attempt to retake the throne, but he was captured and executed by Leo's government. The rebellion was the only serious threat to Leo's usurpation. Umayyad attacks under Caliph Hisham ibn Abd al-Malik continued in the form of yearly raids in eastern and central Asia Minor (see hatched area in figure), which affected communications, commerce and agricultural production. In 721, the city of Dalisandus was captured, followed by the fortresses of Kamachon and Ikonion in 723/724 and several frontier fortresses in 725. Caesarea (Cappadocia) was captured in 727, then Gangra in 728. The Byzantine counter-raids were generally of little strategic impact, although crucially a major invading force was destroyed in the Battle of Akroinon of 740. It was only during the Third Fitna of 744–747, a civil war within the Umayyad Caliphate, that the regularity of attacks were temporarily interrupted.
Leo secured the Empire's frontiers by inviting Slavic settlers into the depopulated districts and by restoring the army to efficiency. His military efforts were supplemented by his alliances with the Khazars and the Georgians. However, the Lombards exploited the Empire's difficulties beginning in 717, when the duke of Benevento captured Cumae, the duke of Spoleto captured Narni and Liutprand, King of the Lombards, occupied Classe in the Exarchate of Ravenna. Although Narni was never regained, Gregory II recovered Cumae and Liutprand withdrew from Classe. In 724 or 725, Leo increased taxes in Italy which Gregory opposed. This led to two plots to assassinate Gregory, the second of which was supported by Exarch Paul, but both were foiled by the Romans with the help of the Lombards of Benevento and Spoleto.
Leo effected many political and ecclesiastical restructurings in order to bolster the authority of the Empire and the Patriarch of Constantinople. Since the end of the seventh century, imperial stratēgoi were sent to the theme of Sicily (which included Calabria), and in 732–733 Leo deprived the church of Rome of the patrimony of St Peter in the theme, reallocating tax income that originally went to the church of Rome to the imperial administration (a large annual sum of 350 pounds of gold). However in 743, Constantine V compensated Pope Zachary for this loss by granting him the estates of Ninfa and Norma to the south of Rome. Between 732 and 754, the bishops of Illyricum, Crete, Sicily, Calabria and Naples (until 769) were transferred from the authority of Rome to Constantinople. The Isaurians in general saw the church and its patriarchs as subordinate to the imperial will.
The 740 Constantinople earthquake damaged the Walls of Constantinople, the restoration of which Leo paid for out of the imperial treasury, raising the City taxes by 81⁄3 per cent in order to do so, as was recorded on the land walls near the Sea of Marmara. The Empire of the eighth century was characterized by ruralization and depopulation, which along with the Arab invasions motivated Leo to undertake intense centralization and militarization, particularly involving the many fortresses and walls in towns such as Nicaea and Padyandus.
Leo III died of dropsy on 18 June 741 and was buried in the Church of the Holy Apostles.
Leo's most striking legislative reforms dealt with religious matters, especially iconoclasm ("icon-breaking," therefore an iconoclast is an "icon-breaker"). After an apparently successful attempt to enforce the baptism of all Jews and Montanists in the empire (722), he issued a series of edicts against the veneration of images (726–729).