Meanwhile the barbarians were coming nearer to the Empire. The Avars demanded tribute, and the Turks, a name that was so soon to be a familiar terror, sent envoys to the Cæsar's court. The enemies, it might seem, were already closing in when Justin became a lunatic, bursting into mad fits of rage, and drawn about the palace in a toy cart, while the "whole senate and city" knew of the sad fate of their Emperor. Sophia, his wife, had all the masterful genius of her aunt Theodora. It was she who gave the rule to Tiberius II., under whom the empire steadily decayed. Maurice, his successor, was a severe ruler, whom the people learned to hate. When at last his reign ended in a revolution and a flight, it was the people of Constantinople, the demes and the factions of the Circus, who gave him to death, and placed the imperial crown on the head of Phocas, his successor.
While Constantinople thus dethroned and set up the civil rulers of the Empire, it was claiming for its patriarch the highest position in the Church. When at the beginning of the sixth century the patriarch John had signed the formula drawn up by Pope Hormisdas, he repudiated any claim to superiority on the part of the old Rome: the two cities and the two Sees he declared were one. As early as 518 the patriarch of Constantinople called himself "universal bishop": in 595 the great Pope Gregory, who had himself, as a papal envoy, seen the greatness of the Eastern See, vigorously protested, to the Emperor Maurice, against the assumption to the title. But while the patriarchs used the title in no exclusive sense, they were determined, as they are determined to-day, to assert the independence of their See and its equality with that of Rome.
Ecclesiastical independence did not preserve the Empire from political weakness. Phocas was soon seen to be worse than Maurice, and one conspiracy after another was begun in the Hippodrome and ended by a massacre in the streets. The Green faction in the Circus called the Emperor a drunkard and a madman to his face. Famine and pestilence ravaged the crowded city, and when Heraclius, already a renowned general, brought his fleet up the Hellespont and anchored at the Golden Horn the collapse of the power of Phocas was immediate, and a new Emperor was crowned in the great church of the "Capital of the World." The reign of Heraclius, gallant man though he was, began in almost unbroken disaster, and when in 615 Jerusalem fell into the hands of the Persians it seemed that the end was at hand. In the next year, as had already happened under Phocas, a Persian army encamped at Chalcedon. When negotiations were in vain, when Heraclius had even formed the idea of transferring the seat of Empire from Constantinople to Carthage, and had only abandoned it after his preparations were far advanced, when the terror and indignation of the people forced him to take oath before the patriarch in S. Sophia that he would never leave "the Queen of Cities," at length the courage of the empire awoke, the nobles sacrificed their wealth and the churches their treasures, the fleet utterly destroyed that of the Persians, and Heraclius delivered the city and the empire by a march as brilliant as it was daring. Leading five thousand veterans across Asia Minor and through the mountains he "penetrated into the heart of Persia and recalled the armies of the great king to the defence of their bleeding country." After three campaigns he returned in triumph and entered, as no Emperor since Theodosius the Great had done, by the Golden Gate.
In his absence thirty thousand Avars, who had swept over the Balkan provinces like a devouring flame, broke through the great wall and encamped under the very walls of the city itself. Churches in the suburbs were burnt to the ground and the famous Church of the Theotokos in Blachernae was on the point of being destroyed, when some panic caused the Avar horsemen to retire. The danger was too obvious for the warning to be neglected, and the Senate, which had refused with contumely the offers of the barbarian leaders, allies of the Persian King, drove back the enemy and immediately increased the fortifications by a new wall. This splendid barrier, magnificent to-day in its ruins, stretched from the enclosure outside the palace of Blachernae, at the foot of the sixth hill, to the Golden Horn. It is flanked by three hexagonal towers.
A year later, in 627, the Emperor, who dreaded even the sight of the sea, crossed the Bosphorus by a bridge of boats, decked with branches of trees to imitate a forest. Landing north of the city he marched inland and crossed the valley at the head of the Golden Horn—below the "Sweet Waters of Europe"—by a bridge made by Justinian nearly opposite the end of the walls. So along the triumphal way he went, past the new walls that have ever since borne his name, and entered by the Golden Gate, the Emperor who had vanquished the Persians, saved his empire, and brought back the greatest of all relics, the sacred wood of the true Cross, which S. Helena, the mother of Constantine, had found on Calvary.
But Heraclius was not to triumph unchecked. The fatal temptation of theological strife conquered even the conqueror of the Persians, and the beginning of the Monothelite controversy dates from the Ekthesis of Sergius the patriarch, a document which, if it were intended to make peace, certainly provoked, war that was not ended, though its area was defined, by the decision of the Fourth General Council, which met at Constantinople in 680, and condemned those who denied that Christ had two wills, human and divine.
The dreary years of the latter half of the seventh century may be rapidly summarised. Constantinople saw the settlement of barbarians, Slaves and Balgars, almost at its gates. Emperor succeeded emperor without anyone appearing who was worthy to be the heir of Heraclius. At length in 672 the Saracens, who had long devastated Asia, brought a fleet up the Hellespont and besieged the city. Their total defeat by Constantine IV., whom his people nicknamed Pogonatus (the bearded), was the greatest triumph of the Christian powers against the infidel; it was won, it is said, by the newly-discovered "Greek fire," so long to be the terror of the foes of the Empire. Constantinople proved herself the bulwark of Europe against the infidel. The nations of the West sent their envoys to applaud. Six hundred years later another Constantine was to fall, when his city was at length captured by the followers of Mohammed.
Justinian II., the son of Constantine Pogonatus, was a great builder like his namesake, whom probably he sought to imitate; but in character he was far from resembling the builder of S. Sophia. In the inimitable phrases of Gibbon, "The name of a triumphant law-giver was dishonoured by the vices of a boy.... His passions were strong; his understanding was feeble; and he was intoxicated with a foolish pride that his birth had given him the command of millions, of whom the smallest community would not have chosen him for their local magistrate. His favourite ministers were two beings the least susceptible of human sympathy, an eunuch and a monk; to the one he abandoned a palace, to the other the finances; the former corrected the Emperor's mother with a scourge, the latter suspended the insolvent tributaries, with their heads downwards, over a slow and smoky fire. Since the days of Commodus and Caracalla, the cruelty of the Roman princes had most commonly been the effect of their fear; but Justinian, who possessed some vigour of character, enjoyed the sufferings and braved the revenge of his subjects about ten years, till the measure was full of his crimes and of their patience."
The attempt to banish a popular general whom he had long imprisoned was the occasion of a revolt which cast the Emperor from the throne; and the hippodrome saw again an act of tragic vengeance, when the tongue and nose of the fallen Cæsar were slit in the presence of the people who had borne with him too long.