Justinian's restoration of the imperial order in the West was short-lived. Indeed, under his successor, his nephew Justin II (565-578), the Empire came under strong pressure. In Italy the Lombards began in 568 the invasion of the northern part of the peninsula and soon a great part of the country came under their control. However, large and strategically located areas in the northern and in the southern regions of the Italian peninsula continued being under Byzantine control. In Spain the Visigoths began their counter-offensive. They took Cordova in 584 and forty years later they succeeded in expelling the imperial administration from Spain. The Empire still held on to its positions in North Africa. These were to stay under imperial administration until the arrival of the Arabs.
In the East, the Persian state continued being the most serious peoccupation of successive Byzantine administrations. In order to counter the Persian threat Justin II's successors, Tiberius-Constantine (578-582) and Maurice (582-602), had to use all the military and diplomatic resources of the Empire. Under Maurice's able administration the state took its first steps which were to lead it into the high middle ages and its most glorious period. Indeed, Maurice's successful attempts to reinforce the remaining western holdings of the Empire constitute the beginning of the complete administrative and military reforms which were to provide the Byzantine state with renewed strength. He created the Exarchates of Ravenna and of Carthage in which the civilian administration and the military command were unified and placed under the authority of a high imperial official, the Exarch.
The creation of the new unified military and administrative units was eventually to become the foundation upon which later Emperors built the military power of the medieval Greek state of the high middle ages. It was during the last years of the 6th century that the Slavs began slowly penetrating south-eastern Europe. Coming possibly from the regions around the Dnieper, following the course of the rivers toward the Black Sea and moving south-west they eventually reached the regions north of the river Danube. Despite repeated attempts by the imperial army to keep the migrant Slavic tribes north of the Danube, by the end of the century it was becoming more difficult to check their advance through the porous and long northern frontier. Finally, the incompetent rule of Phocas (602-610) and the continuous fighting against the Persian armies along the eastern frontier left the northern frontier almost undefended. While, as a result of the Persian advance, the imperial administration was collapsing in the Asiatic provinces, the regions south of the Danube were being occupied by the Slavs and by their powerful, but far less numerous, allies, the Turkic tribe of the Avars. Under tremendous external pressure and in the hands of an incompetent imperial administration the Empire was going through critical moments. Reaction was inevitable and it occurred in October 610. The arrival at Constantinople of the fleet and of the army of the Exarchate of Carthage under the command of Heraclius, son of the Exarch, put and end to Phocas's reign. A new era was beginning.
When Heraclius (610-641) sat on the throne of the Roman Emperors the Empire was facing a deep crisis. His dynamism and persistence during most of his reign, but also the will of the ruling classes and of the people to fight in order to get through the critical moments, contributed to the renaissance of the state. His reign is marked by a profound change in the character of the Roman Empire, as the state was known. The dominant Greek element, which had always been present and formed the cultural and demographic foundation of the state, eventually took over completely and over the years transformed the Roman Empire into a Greek Medieval Empire, which was Roman essentially only by name. Fighting for its survival the Empire ruled by Heraclius had to draw strength from its own resources, human, cultural, ideological and material.
Early in the century and during the early years of the new Emperor's rule the arrival of the Slavic tribes achieved tremendous proportions eventually inundating the northern part of south-eastern Europe and threatening the Greek speaking areas in the south. While the Avars, after pillaging and destroying the areas south of the Danube, even threatening Constantinople, finally moved north of the Danube, the Slavs came to stay. In fact, it appears that the old Romano-Illyrian regions, in the center of the south-eastern European peninsula and in Dalmatia, the north-west of the peninsula and the northern regions of Thrace, in modern Bulgaria, were easily occupied by the newcomers. In those areas, being far more numerous, they absorbed in time the local population. Thus, Salona, the center of the Byzantine administration in Dalmatia, was destroyed around 614, other Dalmatian cities followed soon. Singidunum (Belgrade), Nassus (Nish) and Sardica (Sofia) fell next. However, while the newcomers were able to occupy with relative ease the sparsely populated and mostly romanized areas in the north and in the center of the peninsula, the situation changed when successive waves of migrants reached the densely populated Greek south of the south-European peninsula. There the contact was violent from the beginning. Indeed, the arrival of the Slavic tribes in the Greek lands was followed by violent clashes and heavy fighting.
In many areas the countryside was laid waste, in some regions the invaders were beaten back, while in others, mostly in central Macedonia and in the valley of the river Strymon, they settled down, eventually recognized the imperial authority, adopted Christianity and were in time absorbed by the Greek population. The absence of the bulk of the Byzantine army in the East and the continuous preoccupation of the imperial administration with the effort to stem the Persian onslaught in Eastern Asia Minor, during the 7th century, acted initially in favor of the invaders. In fact Slavic tribal groups penetrated deep, like arrows, into the Greek peninsula. Fighting their way they even reached the Peloponese where they caused widespread destruction and the collapse of authority in the countryside. However, even before the launching of any imperial counter-measures, their successes were checked, from the earliest stages of the invasion, by the presence of the vast network of Greek urban centers, among which Thessaloniki was the most important. Indeed, all Greek cities, both in Macedonia and as far south as the Peloponese, acted as a succession of powerful dams upon which the invasion fell and eventually failed.
Greek peasants, fleeing the dangerous countryside, sought refuge and protection behind the powerful fortifications of the Greek medieval cities, especially in the more exposed Macedonian regions. Behind their strong walls counter-attacks were planned and when eventually the Byzantine state turned its attention to the hard hit areas of the Greek peninsula ideas and projects were laid down on how to bring under control the new-comers, on how to spread Christianity among them, on how to have them recognize imperial authority, on how to assimilate them, on how to transform them from a force of blind destruction to one of participation and of contribution to the medieval civilization of Christian south-eastern Europe and in extension to the civilization of all Europe. In other words on how to introduce them to the medieval Constantinopolitan Roman Christian Oecumene. It was to be a long and stormy process, with crises but also wealthy rewards, which, in the end, with the christianization of Russia gave the full measure of the contribution of medieval Hellenism to the creation of the civilization of Europe.
While the European south-east was being invaded by the Slavs the eastern provinces and their great cities were under tremendous pressure as one after another were being captured by the victorious Persian army. Inevitably, facing the loss of the vital eastern provinces, south-eastern Europe was abandoned to the advancing Slavic tide. Heraclius didn't stay long in Constantinople. Blessed by the Patriarch and reinforced by the prayers of his Christian subjects, he crossed the Bosphorus and marched east, through Asia Minor, leading all the armed forces that the Empire could master at that critical moment in its history. A real crusade was beginning. It was a difficult struggle for the Empire.
The initial counter-offensive failed to stop the Persian advance. In 613 the imperial army suffered a serious setback at Antioch, Damascus fell and was soon followed by the capture of Tarsus by the victorious Persians. In the northern front the Byzantine troops had to evacuate Armenia and then, in 614, Jerusalem fell. When news of the Holy city's loss, of the looting which followed, of the destruction of the church of the Holy Sepulcher and of the carrying away by the Persian troops of the Holy Cross reached Constantinople the psychological effects upon the population and upon the spiritual and civilian rulers of the Empire were shattering. Yet, it was not to be the end of the hardships. Asia Minor was invaded in 615 and the Persian troops reached the shores of the Bosphorus. At the same time Thrace was ravaged by the Slavs and the Avars who soon appeared in front of the imperial capital. Then in 619 the Persian armies began the conquest of Egypt, thus putting an end to the regular shipments of grain (a vestige of the old Roman annona) which was transported to Constantinople for centuries and was used to feed the population of the imperial capital. The end of the supply of Egyptian grain, combined with the anarchy in the European provinces caused by the Slavic invasion, the Avar raids in Thrace and the collapse of imperial authority in vast areas of Asia Minor could eventually bring the Empire to its knees. About that time (624) the Visigoths expelled the Empire from Spain. Only the Balearic islands were still held. The Empire was holding itself together by a thread. Something had to be done soon.
The emperor rejected the thought to abandon Constantinople. Instead, he chose to stay and fight. To help him raise an army the Church gave him its treasures. Heraclius could now (619) afford to pay the Khagan of the Avars large sums of money, sent him distinguished hostages and, at least, buy peace from that quarter. In the meantime the imperial government embarked upon a series of profound administrative and military reforms. Under the circumstances the development of the military branch of the state authority was inevitable. In view of the mutilation of the Empire during the times of Heraclius and the struggle for survival, the military authorities in the areas still held by the imperial armies were invested with full powers which soon overwhelmed the power held by the local civilian administrators. The first steps leading to the complete militarization of the Empire were taken during the critical years of the Persian and Slavic invasions. Consequently, the regions of Asia Minor still under imperial control were divided up by the government into military districts. While the new divisions, resembling the existing Exarchates in Africa and in Italy, were seen as administrative units their character was military and were run by the local army commander, a General (Strategos), whose authority carried from the beginning more weight than the local civilian administrators.
The old provinces were eventually absorbed by the new military districts, which became known as Themes, from the Greek word Qevma meaning the military corps stationed in each one of the new districts. The big units were reinforced by the enlistment of more men and, following the old system of the limitanei, soldiers serving in them were given land, with rights of inheritance, as long as themselves and their descendants served in the army of the Theme. The combination of land acquisition and of military service attracted many settlers in the new districts. There is no doubt also that the newly arrived property owning peasant-soldiers (called stratiotes) reinforced the class of small rural property holders who already lived in the new districts. The presence of a large class of free armed peasants, owners of their lands, and of course fighting to defend them from the enemy became soon the backbone of the defense of the Empire. In the critical centuries that followed the new national army fought valiantly. Enrolled in the armies of the Themes the peasant-soldiers defended their lands, repulsed the enemies and beat back the invaders in Asia Minor and in south-eastern Europe. The thoughtless undermining and the destruction of the system by the short-sighted and selfish policies of the high nobility, during the 11th century, as well as the replacement of the national army by an army of foreign mercenaries, would later precipitated the downfall of the Eastern Roman Empire.
The first Themes were organized in the free areas of Asia Minor. They were the large Themes of the Armeniakoi, in north-eastern Asia Minor, of the Anatolikoi, in central Asia Minor, the Opsikion (from the Latin obsequium), near the Sea of Marmora, and along the coast of southern Asia Minor the maritime Theme of the Caravisianoi. For now the situation in south-eastern Europe was out of control and the only area over which the government was soon able to establish its authority was the one near the capital which became the Theme of Thrace.
Leaving Constantinople in the hands of Patriarch Sergius and his able minister the patrician Bonus, Heraclius left the imperial capital on April 5, Easter Monday, 622. He crossed into Asia Minor where he was met by the newly founded army of the Themes. Summer was spent in training and organizing the new cavalry regiments. In the Autumn the imperial troops moved into Armenia first forcing the Persians to withdraw and then defeating them. When in the Spring of 623 operations resumed the Emperor moved again into Armenia. Fighting was tough and prolonged. A decisive victory was still distant. As a matter of fact Costantinople was seriously threatened during the Summer of 626 by the Avars, who broke their peace with the Emperor, and a Slavic host. At the same time the Persian army, under the command of Schahrbarz, crossed unhindered Asia Minor, captured Chalcedon and camped= on the eastern shore of the Bosphorus, facing Constantinople. Led by the Patriarch, and with religious fervor, the defenders repulsed all attacks and early in August 626, they won a great victory when the great final assault of the enemy failed. The defenders were in no doubt that the God protected capital of the Christian Roman Empire owed its deliverance, from the forces of the heathen enemy, to the Virgin's intervention. This belief and the emotion and exaltation of the defenders are expressed in the words and in the music of one of the most beautiful Hymns of the Greek Church, the Acathistos. Following their defeat the Avars withdrew to the north and from that moment they disappear from the Byzantine annals.
In the Fall of 627 began the Byzantine counter-offensive. In December of the same year the Persian army was defeated near Nineveh and the Byzantine troops advanced into Persia. In the Spring of 628 the Persian king Chosroes was overthrown and his son Kawad Sheroe signed immediately a peace treaty with the Emperor. According to the treaty the Persians returned to the Empire all the Roman provinces which they had occupied during the long war. Thus Armenia, Syria, Roman Mesopotamia, Palestine and Egypt became Roman again. In the Spring of 630 Heraclius visited Jerusalem where to the delight of the Christian population he returned to the Holy city the recovered Holy Cross. It was a fitting end to a holy war. The long war had exhausted the two states. Undoubtedly defeated Persia was in a much worse shape but the Roman state had also suffered important human and material losses. Furthermore the conquest of the old eastern provinces had not solved the acute religious problems between the center of the Empire and the monophysitic eastern populations. The easiness with which the Persian armies had occupied these areas was seen by the central government as a bad omen. The progressive hellenization of the Empire was upset by the ideological split between the Hellenic regions of the Empire, the Greek peninsula and Asia Minor, and the monophysitic east.
Given the above it was necessary for the government, in order to avert a new crisis, to win over the monophysitic populations of the east. The best way to achieve the goal was to reach a compromise between the Chalcedonian official dogma and the eastern heretics. The imperial government and the Emperor, himself, were assisted in their efforts by the energetic participation of the Patriarch of Constantinople. Indeed, based on another eastern doctrine Sergius proposed a solution. Accordingly, the two equal natures of Jesus shared between themselves one activity (ejnevrgeia). The notion of the single activity shared by Jesus's two natures, known as monenergism was pursued energetical by Heraclius and Sergius. While Sergius initiated contacts with eastern clerics, Heraclius, who was still in the east, held talks with local prelates. It appeared that this time the compromise could work. It seems that the Emperor adopted the new doctrine, an event which was favorably greeted in the east where indications point to an agreement for Church union in Armenia, Syria and Egypt. In 631 Cyrus of Phasis, who had close contacts with Sergius, was named Patriarch of Alexandria. He immediately published a pact of union which contained nine chapters on the natures of Jesus and the single activity. It was hoped that the document would be accepted by both Chalcedonians and monophysites. To make the positions contained in the document even stronger, those who rejected it were threatened with excommunication. Emperor Heraclius's, Sergius's and Cyrus's fight to achieve the union was also joined by Pope Honorius, who gave his reserved blessing to the new doctrine, agreeing instead to a single will (qevlhsi") in Jesus.
It was not an easy task. In fact it failed miserably. Resistance from the monophysitic clergy, combined with ferocious reaction to the new heresy by the Chalcedonian prelates, especially from Sophronius, the Patriarch of Jerusalem, caused the collapse of the final attempt to unite east and west. Finally, the Arab conquests and the spread of Islam put an end to the whole issue. However, while the Arab armies were advancing and capturing the eastern provinces and the local Christian populations began converting to Islam, Constantinople continued its efforts to solve the religious problem. Still pursuing the long sought union Sergius abandoned the issue of single activity and turned to the one of single will. The new doctrine of monotheletism became public in late 638, following Sergius's death, in an Ecthesis or exposition of faith which was given the power of imperial edict. The Ecthesis restated the Chalcedonian dogma of the Trinity and of the Incarnation, it abolished the notion of the two activities of the Saviour, and introduced the one of a single will, not to be confused with His two natures. In the vain hope of saving the east, Sergius's successor Pyrrhus, promoted monothelitism. It was attacked from all sides. In Rome Honorius's successors denounced it, the Chalcedonians saw it for what it was, a new heresy, and the monophysites, under the Arabs since 638, rejected it outrightly.
In his old age Heraclius witnessed the collapse of his efforts to restore Roman power in the east. Contrary to Justinian I who died before witnessing the failure of his expensive attempts to rebuild the Roman oecumene, Heraclius's last years were lived in deep depression caused by the total loss of the east to the Arabs, by the inability to control the Slavic crisis in the European provinces, by the unwanted and badly managed religious upheaval and by a simmering dynastic crisis.
The religious and political unification of the Arab world by the Prophet also meant the beginning of the end of the thousand-year old Greek presence in the east. It began with Alexander's conquests in the 4th century B.C., went through the Hellenistic centuries, the Roman presence and its Byzantine extension into the Christian centuries and collapsed militarily on August 20, 636, in the battle of Yarmuk. In that battle the weary Byzantine army was crushed by Caliph Omar's Arab soldiers. As a result of the defeat Byzantine Syria came under Arab administration. Led by Patriarch Sophronius Jerusalem's garrison fought until 638 when it finally surrendered the Holy city to its new master's. Byzantine Mesopotamia fell in 639-640. By then Persia, defeated by Heraclius a short while ago, was conquered by the Arabs.
Assaulted by an unforeseen and cruel destiny the old Emperor passed away in February 641. The Byzantine state's new eastern opponent was the carrier of a new, world conquering, religious ideology, Islam, which was going to challenge and eventually destroy in the 15th century, under its Ottoman version, the medieval Greek state.
Professor of Classical and Byzantine Studies, and Chairman of Hellenic Studies Center at Dawson College, Montreal, and Lecturer at the Department of History at Universite de Montreal, Quebec, Canada.