The Isaurian dynasty is chiefly associated with Byzantine iconoclasm, an attempt to restore divine favour by purifying the Christian faith from excessive adoration of icons, which resulted in considerable internal turmoil.

After successfully overcoming the Sassanid Persians, the Emperor Heraclius (r. 610–641) and his exhausted realm were faced with the sudden onset of the Muslim expansion from Arabia into the Levant.

[1] Following the Muslim conquest of Syria, the rich province of Egypt, the Empire's chief source of grain and tax revenue, had fallen to the Arabs as well.

His successor, Constantine IV (r. 668–685), was able to beat off the First Arab Siege of Constantinople (674–678), and in its aftermath move into the counteroffensive, securing Asia Minor, recovering Cilicia and forcing the Caliphate to pay tribute.

Cilicia was conquered by the Arabs and turned into a base for raiding expeditions that penetrated deep into Asia Minor, sacking its forts and cities, while the Caucasus brought under firm Muslim control.

[4][5] At the same time, the disasters of the 7th century saw major changes in the society and nature of what remained of the Empire: the urbanized, cosmopolitan civilization of Late Antiquity came to an end, and the Medieval era began.

With the decline of most cities to a small, fortified urban cores that functioned merely as administrative centres, society became largely agrarian, while education and intellectual life almost vanished.

The loss of the Empire's richest provinces, coupled with successive invasions, reduced the imperial economy to a relatively impoverished state, compared to the resources available to the Caliphate.

When King Tervel of Bulgaria (who was an ally of Justinian II) invaded Thrace, Bardanes had no choice but to summon the troops of the Opsician Theme to combat the Bulgars.

The choice was hardly based upon his skills; when Leo the Isaurian, strategos of the Anatolic theme, asked the Senate and the Patriarch for his support in becoming emperor, it took little persuading to obtain it.

Leo III, who would become the founder of the so-called Isaurian dynasty, was actually born in Germanikeia in northern Syria c. 685; his alleged origin from Isauria derives from a reference in Theophanes the Confessor, which however may be a later addition.

[12] Following the latter's fall, in 716 Leo allied himself with Artabasdos, the general of the Armeniacs, and was proclaimed emperor while two Arab armies, one under the Caliph's brother Maslamah ibn Abd al-Malik, campaigned in Asia Minor.

Leo averted an attack by Maslamah by clever negotiations, in which he promised to recognize the Caliph's suzerainty, but on 25 March 717, he entered Constantinople and deposed Theodosios.

[13][14][15] Within months, the new Emperor faced his first great challenge, with a massive Muslim attack on the imperial capital: the Caliphate's army and navy, led by Maslamah, numbered some 120,000 men and 1,800 ships according to the sources.

[16] From July 717 to August 718, the city was besieged by land and sea by the Muslims, who built an extensive double line of circumvallation and contravallation on the landward side, isolating the capital.

Their attempt to complete the blockade by sea however failed when the Byzantine navy employed Greek fire against them; the Arab fleet kept well off the city walls, leaving Constantinople's supply routes open.

[18][19] Even during the siege, Leo had been able to stifle attempts at secession: his troops swiftly overthrew a revolt in Sicily, where a certain Basil Onomagoulos was declared emperor.

Following the renewed eruption of Thera in 726, he published an edict condemning their use, and had the image of Christ removed from the Chalke Gate, the ceremonial entrance to the Great Palace of Constantinople.

On the other hand, his introduction of a new and unnecessary theological dispute, albeit for the moment relatively mild, compromised his efforts to restore stability to the Empire.

Constantine was crossing Asia Minor to campaign against the Umayyad Caliphate under Hisham ibn Abd al-Malik on the eastern frontier in June 741 or 742.

Constantine's derogatory epithet Kopronymos ("Dung-named": from kopros, "feces" or "animal dung"; and onoma, "name"), was applied to him by his avowed enemies over this extremely emotional issue, the iconodules.

The council confirmed the status of Mary as Theotokos, or Mother of God, reinforced the use of the terms "saint" and "holy" as meet, and condemned the desecration, burning, or looting of churches in the quest to quench Iconophiles.

Since monasteries tended to be strongholds of Iconophile sentiment, Constantine specifically targeted the monks, pairing them off and forcing them to marry nuns in the Hippodrome and expropriating monastic property for the benefit of the state or the army.

In 746, profiting by the unstable conditions in the Umayyad Caliphate which was falling apart under Marwan II, Constantine invaded Syria and captured Germanikeia (modern Maraş, his father's birthplace).

These campaigns failed to secure any concrete gains (apart from additional population employed to strengthen another frontier), but it is important to note that under Constantine V the Empire had gone on the offensive.

With the resettlement of Christian populations from the East into Thrace, Constantine V aimed to enhance the prosperity and defence of this area which caused concern to the Empire's northern neighbour, Bulgaria, and the two states clashed in 755.

Constantine's campaigns were costly; during his reign the Byzantine Empire's annual revenues were reduced to about 1,800,000 nomismata due to his various wars and the Arab conquests.

Leo was the son of Emperor Constantine V by his first wife, Tzitzak of Khazaria (known as Irene upon her conversion),[35] the daughter of a Khagan of the Khazars (thought to be Bihar).

In addition to the concessionary actions Leo also appointed an iconodule sympathizer, Paul of Cyprus, to the position of patriarch of Constantinople upon the death of the predecessor.

He then divorced his wife Maria of Amnia, who had failed to provide him with a male heir, and married his mistress Theodote, an unpopular and possibly illegal act, although the Patriarch ignored it.