The Byzantine Empire was ruled by the Isaurian dynasty (or Syrian dynasty) from 717 to 802. The Isaurian emperors were successful in defending and consolidating the empire against the caliphates after the onslaught of the early Muslim conquests, but were less successful in Europe, where they suffered setbacks against the Bulgars, had to give up the Exarchate of Ravenna, and lost influence over Italy and the papacy to the growing power of the Franks.
The Isaurian dynasty is chiefly associated with Byzantine iconoclasm, an attempt to restore divine favour by purifying the Christian faith from all veneration of figural Christian iconography, which resulted in considerable internal turmoil.
By the end of the Isaurian dynasty in 802, the Byzantines were continuing to fight the Arabs and the Bulgars for their very existence, with matters made more complicated when Pope Leo III crowned Charlemagne as emperor of the Romans, which was seen as an attempt at making the Carolingian state the successor to the Roman Empire.
Background: Byzantium in the 7th century
The Heraclian dynasty (610–695 and 705–711) faced heavy challenges. 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.Whittow (1996), pp. 73–82
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. The Byzantines also faced Arab attacks through Libya against the Exarchate of Africa, against Cilicia, which controlled the southern passes into Asia Minor, now the Empire's last major contiguous territory, and against the Armenian Highland, the Empire's chief source of manpower and a vital buffer between the now Arab-dominated Syrian Desert region and the northeastern passage into Asia Minor. These three areas would be the main fields of Byzantine-Arab contention during the next half-century.Cheynet (2006), pp. 3–6 The Arabs continued to make headway, most notably constructing a navy that successfully challenged Byzantine supremacy in the Mediterranean. The outbreak of the Muslim civil war in 656 bought the Byzantines time, and emperor Constans II (r. 641–668) reinforced his position in the Balkans and Italy. 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. At the same time however, he was defeated by the Bulgar khan Asparukh, and was forced to accept his people's settlement in Byzantine lands south of the Danube.Cheynet (2006), pp. 6–9 With the first deposition of Constantine IV's son and heir Justinian II in 695 began a period of troubles that lasted almost a quarter-century and brought a succession of disasters that nearly brought about the downfall of the Byzantine state. Carthage finally fell in 697 and a Byzantine recovery attempt defeated next year. 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 was brought under firm Muslim control. Finally, the Umayyad caliph Sulayman ibn Abd al-Malik (r. 715–717) began preparing another huge expedition to conquer Constantinople.Cheynet (2006), pp. 10–12Whittow (1996), p. 138
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 urbanised, cosmopolitan civilisation 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. The monetary economy persisted, but the barter economy experienced a revival as well.Kazhdan (1991), pp. 350–351Whittow (1996), pp. 89–95 Administrative practice also changed: alongside the continued existence of the late Roman provincial system, the surviving field armies were reorganised into the theme system as a means to preserve the remaining imperial territory, although the extensive power concentrated in the hands of the thematic commanders, the strategoi, made them prone to rebel. At the same time, the central bureaucracy in Constantinople also rose in importance.Kazhdan (1991), pp. 351, 2035Whittow (1996), pp. 119–121 In the religious field, the loss of the Monophysite eastern provinces ended the need for the unsuccessful compromise doctrine of Monotheletism, which was abandoned at the Third Council of Constantinople in 680,Cheynet (2006), p. 9 while the Quinisext Council in 692 saw the promotion of the interests and views of the Patriarchate of Constantinople against the See of Rome.Haldon (1990), pp. 73–74
The Empire in crisis, 705–717
After Justinian II's second overthrow, the Byzantine Empire spiralled into another era of chaos matched only by Phocas' mishandling of the last Persian War. Philippikos Bardanes, the Crimean rebel who seized the throne proved to be totally incompetent for rule. Rather than face the looming threat of the Bulgars or the Arabs, he intended to reignite the religious controversies by imposing the much hated Heraclian Monothelitism. 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. Unfortunately for the Emperor, the troops had no loyalty whatsoever to him and after the ritual blinding he was replaced in June 713 by the chief secretary of the Emperor, Artemios.
Artemios was crowned as Anastasios II. Anastasios gave the Empire a brief taste of good leadership, improving the walls of the capital and filling the granaries of the capital to bursting point, in order that the newly reported Arab invasion be dealt with. Every citizen was told to gather enough food for three years for if the Arabs were to reach the straits it would undoubtedly be a lengthy siege. However, Anastasios proved too good for the Empire; in an effort to avert the Arab siege of the Capital, Anastasios planned a preemptive strike against the invaders, using Rhodes as a base. However the Opsician Theme once more revolted and Anastasios found himself in a Thessalonika monastery by 715.
The Opsicians chose Theodosios, an unwilling tax-collector, to rule the Empire. 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 the Isaurian, 717–741 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. After being raised to spatharios by Justinian II, he fought the Arabs in Abasgia, and was appointed as strategos of the Anatolics by Anastasios II.Kazhdan (1991), pp. 1014, 1208 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 recognise the Caliph's suzerainty, but on 25 March 717, he entered Constantinople and deposed Theodosios.Kazhdan (1991), p. 1208Treadgold (1997), p. 345Cheynet (2006), p. 12
Arab siege of Constantinople and its aftermath
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. Whatever the real number, it was a huge force, far larger than the Imperial army. Thankfully for Leo and the Empire, Anastasios II had repaired and strengthened the capital's sea walls. In addition, the Emperor concluded an alliance with the Bulgar khan Tervel, who agreed to harass the invaders' rear.Treadgold (1997), pp. 346–347
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. Forced to extend the siege into winter, the besieging army suffered horrendous casualties from the cold and the lack of provisions.Treadgold (1997), p. 347Cheynet (2006), p. 13 In spring, new reinforcements were sent by the new caliph, Umar ibn Abd al-Aziz (r. 717–720), by sea from Africa and Egypt and over land through Asia Minor. The crews of the new fleets were composed mostly of Christians, who began defecting in large numbers, while the land forces were ambushed and defeated in Bithynia. As famine and an epidemic continued to plague the Arab camp, the siege was abandoned on 15 August 718. On its return, the Arab fleet suffered further casualties to storms and an eruption of the volcano of Thera.Treadgold (1997), pp. 347–349
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. In 719, he also weathered an attempt by the deposed Anastasios II to recover his throne with Bulgar help.Treadgold (1997), pp. 347, 349 Leo further strengthened his position by crowning his wife Maria as Augusta in 718 and his son Constantine as co-emperor in 720.Kazhdan (1991), p. 1209 Profiting from the weakened state of the Caliphate after the enormous losses they had suffered before Constantinople, Leo was able to launch a counter-offensive which achieved some success. The Arabs soon recovered however, and from 720 launched annual raids that devastated large parts of Asia Minor, despite a Byzantine alliance with the Khazars, who launched attacks on the Caliphate's northern flank. Iconium and Caesarea were sacked, and Byzantine troops were again driven out of Armenia.Treadgold (1997), pp. 349–350
Beginning of Iconoclasm
Leo's frustration at his military failures led him to believe, in the fashion of the time, that the Empire had lost divine favour. Already in 722 he had tried to force the conversion of the Empire's Jews, but soon he began to turn his attention to the veneration of icons, which some bishops had come to regard as idolatrous. 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. The Emperor showed himself increasingly critical of the iconophiles, and in a court council in 730 he formally banned depictions of religious figures.Treadgold (1997), pp. 350–353Whittow (1996), pp. 139–142