On the death of Heraclius, his widow Martina invoked his will entrusting the Empire jointly to Constantine (his son by his first marriage), Heraclonas (his younger son) and herself.
On 25th May 641, Constantine, long an invalid, died after a reign of only three months. The people of Constantinople had had enough of Martina's ambition and arrogance - as well as her enthusiastic support of monothelitism. In the summer of 641, in response to increasingly insistent demonstrations, Constantine's eleven year-old son Heraclius was crowned Emperor, and his name changed to Constans; and in September Martina and Heraclonas were arrested. Her tongue was cut out; his nose was slit, and the two were exiled to Rhodes.
The twenty-seven-year reign of Constans II - for the beginning of which the Senate assumed the Regency - was overshadowed by his constant struggle with the Saracens. In 642 Alexandria fell to the Muslim general Amr, who razed the walls and established his new capital at Fostat, now Cairo. Having thus deprived the Empire of its richest province, the conquerors then drove westward along the North African coast and in 647 inflicted a disastrous defeat on the Exarchate of Carthage.
With the accession of the new Caliph Uthman in 644, the Muslims began building a fleet, entrusted to Muawiya, Governor Of Syria. Its first objective was Cyprus, one of the Empire's chief naval bases; the capital Constantia was sacked, the harbour installations destroyed and the surrounding country ravaged. In 654 Muawiya launched a still more formidable expedition and captured the island of Rhodes.
The following year Constans sailed an imperial fleet southward down the coast and met the Saracens off the modern Finike, in Lycia. It was the first of a whole millennium of sea fights between Christian and Muslim, and it was a catastrophe. The Byzantine navy was shattered, and Constans himself escaped only by changing clothes with one of his men.
The Byzantines were given some respite when on 17th June 656 the Caliph Uthman was assassinated in his house at Medina. Ali, the Prophet's son-in-law, was immediately elected in his place. Muawiya, on the other hand, who had been simultaneously proclaimed in Syria, accused Ali of complicity in the murder and swore vengeance. The ensuing strife continued until 661, when Ali's own assassination left Muawiya supreme, thus becoming the first Umayyad caliph.
Meanwhile Constans tried to solve the monothelite controversy by publishing an edict which simply decreed that the whole dispute should be consigned to oblivion. However, the problem persisted, resulting in arrest and detention of Pope Martin.
As the eastern provinces fell to the Arab invaders, Constans's thoughts turned increasingly to the West. In the Balkans, the Slav settlers were growing restive and making difficulties over their annual tribute; in Italy, not surprisingly, Byzantium was more unpopular than ever; Sicily, meanwhile, was under serious threat from the Saracens of North Africa. In 662 Constans decoded to leave Constantinople for good and establish his capital permanently in the West. Having left his family in Constantinople, early in 663 he landed with his army in south Italy and advanced via Naples - a Greek city, and therefore friendly - to Rome where, despite his treatment of Martin, he was accorded a formal welcome by Pope Vitalian; Here he began stripping the city of what few valuables it still possessed - including even the copper from the roof of the Pantheon - and sending them back to Constantinople. In the autumn, having marched south through Calabria, he crossed to Sicily; and for the next five years he kept his court at Syracuse. His end came on 15th September 668; while he was lathering himself in his bath, one of his Greek attendants killed him with the soap-dish.