- Heraclian dynasty and shrinking borders
After Maurice's murder by Phocas, Khosrau used the pretext to reconquer the Roman province of Mesopotamia.Phocas, an unpopular ruler who is invariably described in Byzantine sources as a "tyrant", was the target of a number of senate-led plots. He was eventually deposed in 610 by Heraclius, who sailed to Constantinople from Carthage with an icon affixed to the prow of his ship.Following the accession of Heraclius the Persian advance pushed deep into Asia Minor, also occupying Damascus and Jerusalem and removing the True Cross to Ctesiphon. The counter-offensive of Heraclius took on the character of a holy war, and an acheiropoietos image of Christ was carried as a military standard.Similarly, when Constantinople was saved from an Avar siege in 626, the victory was attributed to the icons of the Virgin which were led in procession by Patriarch Sergius about the walls of the city. The main Persian force was destroyed at Nineveh in 627, and in 629 Heraclius restored the True Cross to Jerusalem in a majestic ceremony. The war had exhausted both the Byzantine and Persian states, and left them extremely vulnerable to the Arab forces which emerged in the following years.The Byzantines suffered a crushing defeat at the Battle of Yarmuk in 636, and Ctesiphon fell in 634.Heraclius as the first emperor to replace the traditional Latin title for his office (Augustus) with the Greek Basileus (Βασιλεύς).This shift from Latin to Greek finds a parallel in the contemporary abandonment of Latin in official documents. In an attempt to heal the doctrinal divide between Chalcedonian and monophysite Christians, Heraclius proposed monotheletism as a compromise. In 638 the new doctrine was posted in the narthex of Hagia Sophia as part of a text called the Ekthesis, which also forbade further discussion of the issue. By this time, however, Syria and Palestine, both hotbeds of monophysite belief, had fallen to the Arabs, and another monophysite center, Egypt, fell by 642. Ambivalence toward Byzantine rule on the part of monophysites may have lessened local resistance to the Arab expansion.Heraclius did succeed in establishing a dynasty, and his descendents held onto the throne, with some interruption, until 711. Their reigns were marked both by major external threats, from the west and the east, which reduced the territory of the empire to a fraction of its 6th-century extent, and by significant internal turmoil and cultural transformationThe Arabs, now firmly in control of Syria and the Levant, sent frequent raiding parties deep into Anatolia, and between 674 and 678 laid siege to Constantinople itself. The Arab fleet was finally repulsed through the use of Greek fire, and a thirty-years' truce was signed between empire and caliphate. The Anatolian raids continued unabated, and accelerated the demise of classical urban culture, with the inhabitants of many cities either refortifying much smaller areas within the old city walls, or relocating entirely to nearby fortresses.The void left by the disappearance of the old semi-autonomous civic institutions was filled by the theme system, which entailed the division of Anatolia into "provinces" occupied by distinct armies which assumed civil authority and answered directly to the imperial administration. This system may have had its roots in certain ad hoc measures taken by Heraclius, but over the course of the seventh century it developed into an entirely new system of imperial governance.The withdrawal of massive amounts of troops from the Balkans to combat the Persians and then the Arabs in the east opened the door for the gradual southward expansion of Slavic peoples into the peninsula, and, as in Anatolia, many cities shrank to small fortified settlements.In the 670s the Bulgars were pushed south of the Danube by the arrival of the Khazars, and in 680 Byzantine forces which had been sent to disperse these new settlements were defeated. In the next year Constantine IV signed a treaty with the Bulgar khan Asparukh, and the new Bulgarian state assumed sovereignty over a number of Slavic tribes which had previously, at least in name, recognized Byzantine rule. In 687/8, emperor Justinian II led an expedition against the Slavs and Bulgars which made significant gains, although the fact that he had to fight his way from Thrace to Macedonia demonstrates the degree to which Byzantine power in the north Balkans had declined.The one Byzantine city that remained relatively unaffected, despite a significant drop in population and at least two outbreaks of the plague, was Constantinople. However, the imperial capital was marked by its own variety of conflict, both political and religious. Constans II continued the monothelete policy of his grandfather, Heraclius, meeting with significant opposition from laity and clergy alike. The most vocal opponents, Maximus the Confessor and Pope Martin I were arrested, brought to Constantinople, tried, tortured, and exiled. Constans seems to have become immensely unpopular in the capital, and moved his residence to Syracuse, Sicily, where he was ultimately murdered by a member of his court. The Senate experienced a revival in importance in the seventh century and clashed with the emperors on numerous occasions. The final Heraclian emperor, Justinian II, attempted to break the power of the urban aristocracy through severe taxation and the appointment of "outsiders" to administrative posts. He was driven from power in 695, and took shelter first with the Khazars and then with the Bulgars. In 705 he returned to Constantinople with the armies of the Bulgar khan Tervel, retook the throne, and instituted a reign of terror against his enemies. With his final overthrow in 711, supported once more by the urban aristocracy, the Heraclian dynasty came to an end.The 7th century was a period of radical transformation. The empire which had once stretched from Spain to Jerusalem was now reduced to Anatolia, Chersonesos, and some fragments of Italy and the Balkans. The territorial losses were accompanied by a cultural shift; urban civilization was massively disrupted, classical literary genres were abandoned in favor of theological treatises, and a new "radically abstract" style emerged in the visual arts. That the empire survived this period at all is somewhat surprising, especially given the total collapse of the Sassanid Empire in the face of the Arab expansion, but a remarkably coherent military reorganization helped to withstand the exterior pressures and laid the groundwork for the gains of the following dynasty.
- Isaurian dynasty and Iconoclasm
Leo III the Isaurian turned back the Muslim assault in 718, and achieved a major victory at the expense of the Arabs in 740. He also addressed himself to the task of reorganizing and consolidating the themes in Asia Minor. His successor, Constantine V, won noteworthy victories in northern Syria, and thoroughly undermined Bulgar strength. In the beginning of the 9th century the Arabs captured Crete, and successfully attacked Sicily, but on September 3, 863, general Petronas attained a huge victory against the emir of Melitene. Under the leadership of Krum the Bulgar threat also reemerged, but in 814 Krum's son, Omortag, arranged a peace with the Byzantine Empire.The 8th and 9th centuries were also dominated by controversy and religious division over Iconoclasm. Icons were banned by Leo and Constantine, leading to revolts by iconodules (supporters of icons) throughout the empire. After the efforts of Empress Irene, the Second Council of Nicaea met in 787, and affirmed that icons could be venerated but not worshipped. Irene is said to have endeavored to negotiate a marriage between herself and Charlemagne, but, according to Theophanes the Confessor, the scheme was frustrated by Aetios, one of her favourites. In 813 Leo V the Armenian restored the policy of iconoclasm, but in 843 Empress Theodora restored the veneration of the icons with the help of Patriarch Methodios. Iconoclasm played its part in the further alienation of East from West, which worsened during the so-called Photian Schism, when Pope Nicholas I challenged Photios' elevation to the patriarchate.
- Macedonian dynasty and resurgence
The Byzantine Empire reached its height under the Macedonian emperors of the late 9th, 10th, and early 11th centuries, when it gained control over the Adriatic Sea, southern Italy, and all of the territory of tsar Samuil of Bulgaria. The cities of the empire expanded, and affluence spread across the provinces because of the new-found security. The population rose, and production increased, stimulating new demand while also helping to encourage trade. Culturally, there was considerable growth in education and learning. Ancient texts were preserved and patiently re-copied. Byzantine art flourished, and brilliant mosaics graced the interiors of the many new churches.Though the empire was significantly smaller than during the reign of Justinian, it was also stronger, as the remaining territories were less geographically dispersed and more politically and culturally integrated.Although traditionally attributed to Basil I (867–886), initiator of the Macedonian dynasty, the "Byzantine renaissance" has been more recently ascribed to the reforms of his predecessor, Michael III (842–867) and his wife's counsellor, the erudite Theoktistos. The latter in particular favoured culture at the court, and, with a careful financial policy, steadily increased the gold reserves of the Empire. The rise of the Macedonian dynasty coincided with internal developments which strengthened the religious unity of the empire.The iconoclast movement was experiencing a steep decline: this favoured its soft suppression by the emperors and the reconciliation of the religious strife that had drained the imperial resources in the previous centuries. Despite occasional tactical defeats, the administrative, legislative, cultural and economic situation continued to improve under Basil's successors, especially with Romanos I Lekapenos (920–944). The theme system reached its definitive form in this period. The church establishment began to loyally support the imperial cause, and the power of the landowning class was limited in favour of agricultural small holders, who made up an important part of the military force of the Empire. These favourable conditions contributed to the increasing ability of the emperors to wage war against the Arabs.
