This world was shattered by successive invasions, which resulted in extensive territorial losses, financial collapse and plagues that depopulated the cities, while religious controversies and rebellions further weakened the Empire.

After a long and exhausting struggle, Heraclius managed to defeat the Persians and restore the Empire, only to lose these provinces again shortly after to the sudden eruption of the Muslim conquests.

The combined effect of an army revolt led by a junior officer named Phocas and major uprisings by the Greens and Blues forced Maurice to abdicate.

[6] The Persian King Khosrau II responded by launching an assault on the Empire, ostensibly to avenge Maurice, who had earlier helped him to regain his throne.

[7] Due to the overwhelming crisis facing the Empire that had pitched it into chaos, Heraclius the Elder now attempted to seize power from Phocas in an effort to better Byzantium's fortunes.

Their sweeping movement into Dalmatia engulfed several Byzantine cities, namely Singidunum (Belgrade), Viminacium (Kostolac), Naissus (Niš), Sardica (Sofia), and destroyed Salona in 614.

[8] To recover from a seemingly endless number of defeats, Heraclius went about a reconstruction plan of the military, financing it by fining those accused of corruption, increasing taxes, and debasing the currency to pay more soldiers and forced loans.

[14] Heraclius decided to negotiate a peace with the Avars and Slavs by paying them a large amount of tribute so that he could freely move his armies from Europe to Asia in order to launch counter-offensives against the Persians.

He sailed his newly created army down the Ionian coast and landed at Issus, the exact site where Alexander the Great had decisively defeated the Persians some 1,000 years prior.

Burning numerous cities of his opponents, Heraclius made a risky decision and led his troops deep within the heartland of the Sassanid Empire to Ctesiphon, the Persian capital.

However, a sandstorm blew on 20 August 636 against the Byzantines and when the Arabs charged against them they were utterly annihilated:[22] The Battle fought at Yarmuk was of the fiercest and bloodiest kind ... the Romans and their followers tied themselves to each other by chains, so that no one might set his hope to flight.

By Allah's help some 70,000 of them were put to death and their remnants took to flight ...Jerusalem surrendered to the Arabs in 637, following a stout resistance; in 638, the Caliph Omar rode into the city.

It was Heraclius who first withdrew the eastern field armies into Anatolia, sowing the seeds of the Theme system, and it was he who, through depopulation and the razing of fortifications, stabilized the Anatolian frontier, which would remain largely unchanged for the next 350 years.

By Heraclius's late reign, proper Latin had been reduced to a military and ceremonial role outside of the Exarchates, replaced by Greek as the language of court and high administration.

However, his lengthy life meant that the Byzantines remembered him for his religious controversies, failures against the Arabs, and incestuous marriage to his niece, which many believed to have brought divine retribution upon the entire Empire.

After his death, Heraclius' corpse remained unburied for three days, guarded by his soldiers until it was laid to rest in the Church of the Holy Apostles within a sarcophagus of white onyx next to the founder of his Empire, Constantine I.

Constans II had inherited from his grandfather Heraclius the war with the Arabs, who were bent on conquering the Byzantine Empire and spreading the word of the Islamic Prophet Muhammad.

In 648, Constans still only 18 years of age, declared an edict that no one would raise the monothelitism versus Chalcedon controversy under the pain of banishment, following an excommunication by the Pope Theodore I to the Patriarch of Constantinople Pyrrhus.

[30] When Theodore's successor, Martin I once again added fuel to the fire by summoning a council in condemnation of Monethelitism in October 648, he was arrested, brought to the capital and badly mistreated as a common criminal.

Whilst the Saracens were establishing themselves in former Byzantine territory, the Avars and Bulgars still remained along the Danube river, as did the Slavs, whose annual payment to the Empire was falling short.

The Byzantine-Arab wars became increasingly one-sided and the immense resources of the Caliphate meant that any reconquest was now remotely unlikely — and more so whilst disunity through dissatisfied peasants and restless Bishops lingered on.

The Byzantine historian Theophylact Simocatta, writing during the reign of Heraclius (r. 610–641), relayed information about China's geography, its capital city Khubdan (Old Turkic: Khumdan, i.e. Chang'an), its current ruler Taisson whose name meant "Son of God" (Chinese: Tianzi, although this could be derived from the name of Emperor Taizong of Tang), and correctly pointed to its reunification by the Sui dynasty (581–618) as occurring during the reign of Maurice, noting that China had previously been divided politically along the Yangzi River by two warring nations.

Calling forth representatives from all corners of Christendom to discuss the matter at hand, they debated until in 681 when Constantine IV, who had presided over much of the meetings, endorsed the virtually unanimous findings.

As it would turn out, his name would dictate his foreign policy in an attempt to emulate Justinian I's conquest of the West — a risky move considering what few resources the Empire had to defend herself.

The benefit of the move was twofold—in addition to opening up more agricultural land, there would also have been an increase in the population and a larger number of Thematic militia troops could be raised — allowing the Empire to wage war with more.

Marching on to the Hagia Sophia, he was fortunate enough to find the support of the Patriarch Callinicus I—whose recent insults to the incumbent Emperor left him in fear of his life and with little choice.

[47] With the support of the fanatical Hippodrome Blue team, Leontius and his men overthrew Justinian II, cutting his nose off in the oriental process of rhinokopia and declaring himself as Basileus.

[47] Tiberius' rule was similarly short but slightly more impressive for his successful campaigning against the Saracens—indeed it seems that his Germanic heritage had given him the same appetite for war that had allowed many of his "barbarian" kind to conquer the Western Empire, with his troops reaching into Armenia and even Muslim-held Syria.

With him and his staff of officers dead, Byzantium's neighbours lost no time in exploiting the weakened army—suffering major defeats against the barbarian tribes near the mouth of the Danube and losing the vital stronghold of Tyana in Cappadocia.

Therefore, in a similar case to Leontius and Tiberius' usurpation, he defected and, with the army and navy under his command, declared his support for the renegade Bardanes, who changed his name to Philippicus.