But the favourable terms of the peace which had been concluded did not please the latter’s stepsons,  unable as they were to protect the Greek armies. They decided that Romanus should not return to the imperial throne. When Diogenes learned that they had become his enemies, he prepared to wage civil war  against them, trusting in the help of the Persians. Seeing that they were unable to resist him, his stepsons tried to trick him through a treacherous peace. They sent to him carrying messages of peace twelve bishops, who were themselves ignorant of the deception, as well as Joscelyn,  for whom Romanus had many times showed his love and whom he had no hesitation in trusting as a friend. Romanus believed Joscelyn and the bishops, being reassured when they swore an oath and gave him the assurances which he sought. He believed, in vain, that he would return as emperor; however,  as soon as he had come to Heraclea he was seized and then blinded. Thus it was that this man of noble repute who had been emperor became a monk.
The two brothers were now safe and held the reins of the empire in peace. Their tyranny did not however remain unpunished. For Romanus’ son took as his allies the Armenians and Persians and deprived the empire of its eastern lands, which he ravaged with fire and sword.  From this time onwards the wicked Persian race began to invade the Roman Empire, slaughtering and robbing. The land could not indeed have remained until now subject to imperial rule had not the Gallic race, more warlike and powerful than any other people, and encouraged by divine command, defeated the enemy and given it back its freedom. Inspired by God they wanted to open the roads to the Holy Sepulchre,  previously and for a long time blocked. The wretched men by whose advice this great man had been blinded were arrested, expelled from the court and made to submit to well-merited retribution. They ordered that those who had formerly punished the innocent  should themselves be punished for their guilt with a variety of torments.
An ambassador from Bari was sent to Constantinople and begged the emperor to aid its wretched citizens. On his order pirate ships were suitably prepared to transport grain  and arms [also] by which the fleet could be protected during the voyage to the city. (Hence the sailors would be freed from fear and the city from want). The emperor ordered that Joscelyn be put in command of this fleet. He had fled from Italy in fear of the duke, who hated him because he had conspired against him.  Joscelyn came in haste with his warships to encourage the tremulous citizens. He was already close to the city, hoping to enter it in safety during the night, when suddenly Robert’s fleet encountered the Greek fleet which had come to strengthen his enemies.  The duke’s ships willingly entered on a night action, thinking that this was more favourable to them than to the enemy since they knew these waters while their opponents did not. After a great deal of effort Joscelyn’s ship was defeated and captured, and he himself brought prisoner before the duke.  Another Greek ship was sunk, the rest just managed to escape.
The Norman race had up to this point known nothing of naval warfare. But by thus returning victorious they very much enhanced their leader’s confidence, for he knew that the Greeks had been unable to carry enough help to the citizens of the town to hinder the siege.  At the same time, he greatly rejoiced at the novelty of this naval victory, hoping in consequence that he and the Normans might in future engage in battle at sea with more hope of success.  Joscelyn led an unhappy life shut up in prison for a long time; he went through much travail and his sufferings continued until the end of his life.
The town underwent its third year of siege. Finally it was overcome, worn down by many woes, but above all by hunger. The leading citizen of the town was at this time Argyritzos.  When the duke convinced him that the city must be surrendered, he did not [then] face a difficult task in overcoming the rest of its inhabitants, for the leading men were able to influence the minds of the lesser to persuade them to do as they wanted. Robert showed kindness and favour to the citizens  and since he always cherished those whom he had made his subjects, he himself was loved by all of them. The duke returned to the townspeople most of what had been taken from them by force or ruse:  fields, estates and farms. He restored what had been lost, and made no impositions on the citizens, nor did he permit others to inflict burdens upon them. He now gave peace and freedom to those who had been accustomed to pay tribute to the Normans of the surrounding areas. He pitied the white hair of Stephan  and was unwilling to treat him as an enemy; rather he forgot that the latter had tried to have him murdered and was anxious to treat him kindly. To the surprise of many of the Greeks, when he was captured along with Bari the duke left him free and unpunished, although under surveillance. After remaining in the city for some days the conqueror ordered the Bariots to prepare arms and supplies, and to follow him to wherever they saw him go.  He [then] led them with his own troops to the city of Reggio.
 Despite the defeat, Byzantine casualties were apparently relatively low. Ducas had escaped with no casualties and quickly marched back to Constantinople where he led a coup against Romanus. Bryennius also lost few men in the rout of his wing. Since the battle had not occurred until after nightfall, the Turks did not pursue the fleeing Byzantines, which probably saved most of them. The Turks did not even recapture Manzikert itself at this point. The Byzantine army regrouped and marched to Dokeia, where they were joined by Romanus when he was released a week later.
 Joscelyn was an important figure at Romanus’ court but was captured by Guiscard at Bari in February 1071. For him to have played a role in the betrayal of Diogenes, he must have been freed by Guiscard possibly with the Greek prisoners freed after the fall of Palermo in 1072. William of Apulia is the only source to mention his treachery.
 Once the capture of Diogenes was known in Constantinople, he was deposed, Eudocia exiled and Muchael VII proclaimed emperor. On being freed, Diogenes sought to reclaim the empire and assembled a strong army in Armenia including many of the Normans (but not Robert Crispin) and moved into Cappadocia before retreating to Cilicia, with the Armenian Chatchatour, catepan of Antioch in the autumn of 1072 to await support from Alp Arslan. Besieged in Adana, he surrrendered to Andronicus Ducas on good terms but was betrayed at Heraclea and blinded. He died soon after as a result.
 Michael VII was himself deposed in 1078 becoming a monk and then a bishop; John Ducas was exiled in 1073 becoming a monk.
 The usurpation of Andronicus Ducas also politically destabilised the empire and it was difficult to organise a resistance to the Turkish migrations that followed Manzikert. Within the next few decades, almost all of Asia Minor was overrun by the Seljuks.
 Malaterra attributed the victory and the capture of Joscelyn to Roger.
 By August 1068, Robert Guiscard was finally ready to move against Byzantine Apulia and to begin his most ambitious military operation: the siege of Bari. This was a difficult operation and could only be attempted when Robert had the full support of his Norman vassals. Count Roger also temporarily abandoned his conquest of Sicily to take part in the later stages of the attack on the city. Bari was a trading city with access to the sea for reinforcements and supplies from the Byzantine Empire and was strongly defended on the landward side. However, the Normans were by this time well versed in siege warfare. Bari was not prepared to surrender as, for example Reggio had been in 1060. Bari proved to be a formidable obstacle though the timing of Robert’s attack was fortuitous. By 1068, the situation on the eastern frontier of the Byzantine Empire was critical. Turkish raids had penetrated into Asia Minor and the emperor Romanus IV was determined to do something about this. The situation in Byzantine Italy was severe but it was not seen as a major priority in Constantinople. Even so, the siege of Bari lasted almost three years. Robert recruited ships and sailors from Calabria to blockade the town from the sea and he also was highly successful in exploiting divisions within Bari itself. The Byzantines made two attempts to break the blockade: in 1068 they were partially successful bringing in supplies so prolonging the siege but in 1071 the Byzantine fleet was intercepted from count Roger with ships from Sicily and defeated. The loss of this supply fleet led to Bari’s surrender on 15th April 1071. Although the city was near to starvation, Robert offered generous terms returning land seized from its inhabitants outside the walls, freeing it from tribute that had previously been paid to the Normans and refraining from imposing any new demands. It seems that the local patriciate remained largely in control of the city. Robert almost certainly had no choice but to do this. Bari was a large and prosperous town with a diversified economy that he needed to remain prosperous; coercion was not really a viable economic or political option.
 Argyritzos was the leader of the pro-Guiscard faction in Bari. Helped by the shortage of food, he was able to persuade the city to surrender on 15th April 1071.
 There is some disagreement among historians about the significance of the generous terms offered to Bari. Gay, Jules, L’Italie meridionale a l’empire byzantin depuis l’avènement de Basile Ier jusqu’a la prise de Bari par les Normandes, Paris, 1904 p. 538 argues persuasively that Guiscard sought to protect Bari against the advances of Normans already established in the area while Chalandon, F., Histoire de la domination normande en Italie et en Sicile, Paris, 1907, vol. I, p. 189 and Delarc, O., Les Normandes en Italie depuis les premières invasions jusqu’ l’avènement de S. Grégorie VII, Paris, 1883, p. 454 prefer the explanation that the tribute Bari paid to Constantinople was redistributed among the Normans.
 Guiscard left Bari in May 1071 and stayed in Otranto in June and July. Amatus said that he sent his fleet while he travelled by land with his cavalry.