Following a period of relative success and expansion under the Macedonian dynasty (c. 867–c. 1054), Byzantium experienced several decades of stagnation and decline, which culminated in a vast deterioration in the military, territorial, economic and political situation of the Byzantine Empire by the accession of Alexios I Komnenos in 1081.

The problems the empire faced were partially caused by the growing influence and power of the aristocracy, which weakened the empire's military structure by undermining the theme system that trained and administered its armies. The remnants of the once-formidable armed forces were allowed to decay, to the point where they were no longer capable of functioning as an army.

The simultaneous arrival of aggressive new enemies – Turks in the east and Normans in the west – was another contributory factor. In 1040, the Normans, originally landless mercenaries from northern parts of Europe in search of plunder, began attacking Byzantine strongholds in southern Italy. The Seljuk Turks conducted a series of damaging raids into Armenia and eastern Anatolia – the main recruiting ground for Byzantine armies. The Battle of Manzikert in 1071 would eventually result in the total loss of Byzantine Anatolia.

Isaac and Alexios Komnenos conducts a coup against Nikephoros III Botaneiates. Alexios and his forces broke through the walls of Constantinople on 1 April 1081 and sacked the city; Patriarch Cosmas convinced Nikephoros to abdicate to Alexios rather than prolong the civil war. Alexios becomes the new Byzantine Emperor.

At the very outset of his reign, Alexios was faced with multiple problems. He had to meet the formidable threat of the Normans under Robert Guiscard and his son Bohemond of Taranto. Also, taxation and the economy were in complete disarray. Inflation was spiralling out of control, the coinage was heavily debased, the fiscal system was confused (there were six different nomismata in circulation), and the imperial treasury was empty. In desperation, Alexios had been forced to finance his campaign against the Normans by using the wealth of the Eastern Orthodox Church, which had been put at his disposal by the Patriarch of Constantinople.

The Normans used the deposition of the previous emperor Michael by Nicephorus Botaneiates as the casus belli to invade the Balkans. This gave Robert a motive to invade the empire claiming his daughter had been mistreated.

The Battle of Dyrrhachium was fought between the Byzantine Empire, led by the Emperor Alexios I Komnenos, and the Normans of southern Italy under Robert Guiscard, Duke of Apulia and Calabria. The battle ended in a Norman victory and was a heavy defeat for Alexios. Historian Jonathan Harris states that the defeat was "every bit as severe as that at Manzikert." He lost about 5,000 of his men, including most of the Varangians. Norman losses are unknown, but John Haldon claims they are substantial as both wings broke and fled.

Alexios bribed the German king Henry IV with 360,000 gold pieces to attack the Normans in Italy, which forced the Robert Guiscard and the Normans to concentrate on their defenses at home in 1083–84. Alexios also secured the alliance of Henry, Count of Monte Sant'Angelo, who controlled the Gargano Peninsula.

On 3 November 1082, the Normans besieged the city of Larissa. In the early winter of 1082, Alexios managed to obtain a mercenary force of 7,000 soldiers from the Seljuk Turkish sultan Suleiman ibn Qutulmish. The contingent was led by a general named Kamyres. Alexios continued to raise troops in Constantinople. In March 1083, Alexios departed from Constantinople at the head of an army which marched towards Larissa.

In July, Alexios attacked the blockading force, harassing it with mounted Turkish archers and spreading discord among its ranks through diplomatic techniques. The demoralized Normans were forced to break off the siege. Discord continued to spread in the Norman army, as its officers demanded two and half years worth of payment arrears, a sum Bohemond did not possess. The bulk of the Norman army returned to the coast and sailed back to Italy, leaving only a small garrison at Kastoria.

Meanwhile, Alexios granted the Venetians a commercial colony in Constantinople, as well as exemption from trading duties in return for their renewed aid. They responded by recapturing Dyrrhachium and Corfu and returning them to the Byzantine Empire. The death of Robert Guiscard in 1085 and these victories returned the Empire to its previous status quo and marked the beginning of the Komnenian restoration.

In 1087, Alexios faced a new invasion. This time the invaders consisted of a horde of 80,000 Pechenegs from north of the Danube, and they were heading for Constantinople. Alexios crossed into Moesia to retaliate but failed to take Dorostolon. During his retreat, the emperor was surrounded and worn down by the Pechenegs, who forced him to sign a truce and to pay protection money. In 1090 the Pechenegs invaded Thrace again, while Tzachas, the brother-in-law of the Sultan of Rum, launched a fleet and attempted to arrange a joint siege of Constantinople with the Pechenegs. Without enough troops to repel this new threat, Alexios used diplomacy to achieve a victory against the odds. Alexios overcame this crisis by bribing a horde of 40,000 Cumans, with whose help he surprised and annihilated the Pechenegs at the Battle of Levounion in Thrace on 29 April 1091.

This put an end to the Pecheneg threat, but in 1094 the Cumans began to raid the imperial territories in the Balkans. Led by a pretender claiming to be Constantine Diogenes, a long-dead son of the Emperor Romanos IV, the Cumans crossed the mountains and raided into eastern Thrace until their leader was eliminated at Adrianople. With the Balkans more or less pacified, Alexios could now turn his attention to Asia Minor, which had been almost completely overrun by the Seljuk Turks.

From 1088, Tzachas used his base at Smyrna to wage war against the Byzantines. Employing Christian craftsmen, he built a fleet, with which he captured Phocaea and the eastern Aegean islands of Lesbos (except for the fortress of Methymna), Samos, Chios and Rhodes. A Byzantine fleet under Niketas Kastamonites was sent against him, but Tzachas defeated it in battle. Some modern scholars have speculated that his activities during this time may have been in conjunction, and perhaps even coordination, with two contemporary Byzantine rebels, Rhapsomates in Cyprus, and Karykes in Crete.

In 1090/91, the Byzantines under Constantine Dalassenos recovered Chios. Undeterred, Tzachas rebuilt his forces, and resumed his attacks. In 1092, Dalassenos and the new megas doux, John Doukas, were sent against Tzachas, and attacked the fortress of Mytilene on Lesbos. Tzachas resisted for three months, but finally had to negotiate a surrender of the fortress. During his return to Smyrna, Dalassenos attacked the Turkish fleet, which was almost destroyed.

Despite his improvements, Alexios did not have enough manpower to recover the lost territories in Asia Minor. Having been impressed by the abilities of the Norman cavalry at Dyrrhachium, he sent ambassadors west to ask for reinforcements from Europe. This mission was deftly accomplished – at the Council of Piacenza in 1095, Pope Urban II was impressed by Alexios's appeal for help, which spoke of the suffering of the Christians of the east and hinted at a possible union of the eastern and western churches.

On 27 November 1095, Urban II called together the Council of Clermont in France. There, amid a crowd of thousands who had come to hear his words, he urged all present to take up arms under the banner of the Cross and launch a holy war to recover Jerusalem and the east from the 'infidel' Muslims. Indulgences were to be granted to all those who took part in the great enterprise. Many promised to carry out the Pope's command, and word of the Crusade soon spread across western Europe. Alexios had anticipated help in the form of mercenary forces from the West, and was totally unprepared for the immense and undisciplined hosts which soon arrived, to his consternation and embarrassment.

The "Prince's Crusade", gradually made its way to Constantinople, led in sections by Godfrey of Bouillon, Bohemond of Taranto, Raymond IV of Toulouse, and other important members of the western nobility. Alexios used the opportunity to meet the crusader leaders separately as they arrived, extracting from them oaths of homage and the promise to turn over conquered lands to the Byzantine Empire.

Transferring each contingent into Asia, Alexios promised to supply them with provisions in return for their oaths of homage. The crusade was a notable success for Byzantium, as Alexios recovered a number of important cities and islands. The siege of Nicaea by the crusaders forced the city to surrender to the emperor in 1097, and the subsequent crusader victory at Dorylaeum allowed the Byzantine forces to recover much of western Asia Minor.

John Doukas re-established Byzantine rule in Chios, Rhodes, Smyrna, Ephesus, Sardis, and Philadelphia in 1097–1099. This success is ascribed by Alexios' daughter Anna to his policy and diplomacy, but by the Latin historians of the crusade to his treachery and deception.

Despite his many successes, during the last twenty years of his life Alexios lost much of his popularity. This was largely due to the harsh measures he was forced to take in order to save the embattled empire. Conscription was introduced, causing resentment among the peasantry, despite the pressing need for new recruits to the imperial army.

In order to restore the imperial treasury, Alexios took measures to tax the aristocracy heavily; he also cancelled many of the exemptions from taxation that the church had previously enjoyed. In order to ensure that all taxes were paid in full, and to halt the cycle of debasement and inflation, he completely reformed the coinage, issuing a new gold hyperpyron (highly refined) coin for the purpose. By 1109, he had managed to restore order by working out a proper rate of exchange for the whole coinage. His new hyperpyron would be the standard Byzantine coin for the next two hundred years.

The final years of Alexios's reign were marked by persecution of the followers of the Paulician and Bogomil heresies—one of his last acts was to burn at the stake the Bogomil leader, Basil the Physician; by renewed struggles with the Turks (1110–1117).

After the failure of the Crusade of 1101, the Seljuq and Danishmend Turks resumed their offensive operations against the Byzantines. Following their defeats, the Seljuqs under Malik Shah had recovered control of central Anatolia, re-consolidating a viable state around the city of Iconium. Emperor Alexios I Komnenos, aged and suffering from an illness which proved to be terminal, was unable to prevent Turkish raids into the recovered areas of Byzantine Anatolia, though an attempt to take Nicaea in 1113 was thwarted by the Byzantines. In 1116 Alexios was able to personally take the field and was engaged in defensive operations in northwest Anatolia.

The Seljuk forces attacked the Byzantine army a number of times to no effect. Having suffered losses to his army in the course of these attacks, Malik Shah sent to Alexios a proposal for peace involving a cessation of Turkish raids. The campaign was remarkable for the high level of discipline shown by the Byzantine army. Alexios had demonstrated that he could march his army with impunity through Turkish dominated territory.

The accession of John was contested. As Alexios lay dying in the monastery of the Mangana on 15 August 1118, John, relying on trusted relatives, especially his brother Isaac Komnenos, gained entry into the monastery and obtained the imperial signet ring from his father. He then assembled his armed followers and rode to the Great Palace, gathering the support of the citizenry on the way. The palace guard at first refused to admit John without clear proof of his father's wishes, however, the mob surrounding the new emperor simply forced an entry. In the palace John was acclaimed emperor. Irene, taken by surprise, was unable either to persuade her son to step down, or to induce Nikephoros to contend for the throne.

Alexios died the night following his son's decisive move to take power. John refused to attend his father's funeral, despite the pleas of his mother, because he feared a counter-coup. However, in the space of a few days, his position seemed secure. Within a year of his accession, however, John II uncovered a conspiracy to overthrow him which implicated his mother and sister. Anna's husband Nikephoros had little sympathy with her ambitions, and it was his lack of support which doomed the conspiracy. Anna was stripped of her property, which was offered to the emperor's friend John Axouch. Axouch wisely declined and his influence ensured that Anna's property was eventually returned to her and that John II and his sister became reconciled, at least to a degree. Irene retired to a monastery and Anna seems to have been effectively removed from public life, taking up the less active occupation of historian.

In 1122, Pechenegs from the Pontic steppes invaded the Byzantine Empire by crossing the Danube frontier into Byzantine territory. According to Michael Angold, it is possible that their invasion took place with the connivance of Vladimir Monomakh (r. 1113–1125), the ruler of Kiev, given that the Pechenegs had once been his auxiliaries. It is recorded that the remnants of the Oghuz and the Pechenegs had been expelled from Russia in 1121. The invasion posed a serious threat to Byzantine control over the northern Balkans. Emperor John II Komnenos of Byzantium, determined to meet the invaders in the field and drive them back, transferred his field army from Asia Minor (where it had been engaged against the Seljuk Turks) to Europe, and prepared to march north.

The Byzantine victory effectively destroyed the Pechenegs as an independent force. For some time, significant communities of Pechenegs remained in Hungary, but eventually the Pechenegs ceased to be a distinct people and were assimilated by neighbouring peoples such as the Bulgarians and Magyars. For the Byzantines, the victory did not immediately lead to peace since the Hungarians attacked Branitshevo, the Byzantine outpost on the Danube, in 1128. Yet, the victory over the Pechenegs, and later the Hungarians, ensured that much of the Balkan peninsula would remain Byzantine, allowing John to concentrate on extending Byzantine power and influence in Asia Minor and the Holy Land.

After his accession, John II had refused to confirm his father's 1082 treaty with the Republic of Venice, which had given the Italian republic unique and generous trading rights within the Byzantine Empire. Yet the change in policy was not motivated by financial concerns. An incident involving the abuse of a member of the imperial family by Venetians led to a dangerous conflict, especially as Byzantium had depended on Venice for its naval strength. After a Byzantine retaliatory attack on Kerkyra, John exiled the Venetian merchants from Constantinople. But this produced further retaliation, and a Venetian fleet of 72 ships plundered Rhodes, Chios, Samos, Lesbos, Andros and captured Kefalonia in the Ionian Sea. Eventually John was forced to come to terms; the war was costing him more than it was worth, and he was not prepared to transfer funds from the imperial land forces to the navy for the construction of new ships. John re-confirmed the treaty of 1082, in August 1126.

John's marriage to the Hungarian princess Piroska involved him in the dynastic struggles of the Kingdom of Hungary. In giving asylum to Álmos, a blinded claimant to the Hungarian throne, John aroused the suspicion of the Hungarians. The Hungarians, led by Stephen II, then invaded Byzantium's Balkan provinces in 1127, with hostilities lasting until 1129. The Hungarians attacked Belgrade, Nish and Sofia; John, who was near Philippopolis in Thrace, counterattacked, supported by a naval flotilla operating on the Danube. After a challenging campaign, the details of which are obscure, the emperor managed to defeat the Hungarians and their Serbian allies at the fortress of Haram or Chramon, which is the modern Nova Palanka. Following this the Hungarians renewed hostilities by attacking Braničevo, which was immediately rebuilt by John. Further Byzantine military successes, Choniates mentions several engagements, resulted in a restoration of peace. The Danube frontier had been definitively secured.

In the Levant, the emperor sought to reinforce Byzantine claims to suzerainty over the Crusader States and to assert his rights over Antioch. In 1137 he conquered Tarsus, Adana, and Mopsuestia from the Principality of Armenian Cilicia, and in 1138 Prince Levon I of Armenia and most of his family were brought as captives to Constantinople.This opened the route to the Principality of Antioch, where Raymond of Poitiers, Prince of Antioch, and Joscelin II, Count of Edessa, recognized themselves as vassals of the emperor in 1137. Even Raymond II, the Count of Tripoli, hastened northwards to pay homage to John, repeating the homage that his predecessor had given John's father in 1109.

Freed from immediate external threats in the Balkans or in Anatolia, having defeated the Hungarians in 1129, and having forced the Anatolian Turks on the defensive, the Byzantine emperor John II Komnenos could direct his attention to the Levant, where he sought to reinforce Byzantium's claims to suzerainty over the Crusader States and to assert his rights and authority over Antioch.

Control of Cilicia opened the route to the Principality of Antioch for the Byzantines. Faced with the approach of the formidable Byzantine army, Raymond of Poitiers, prince of Antioch, and Joscelin II, count of Edessa, hastened to acknowledge the Emperor's overlordship. John demanded the unconditional surrender of Antioch and, after asking the permission of Fulk, King of Jerusalem, Raymond of Poitiers agreed to surrender the city to John.

The siege of Shaizar took place from April 28 to May 21, 1138. The allied forces of the Byzantine Empire, Principality of Antioch and County of Edessa invaded Muslim Syria. Having been repulsed from their main objective, the city of Aleppo, the combined Christian armies took a number of fortified settlements by assault and finally besieged Shaizar, the capital of the Munqidhite Emirate. The siege captured the city, but failed to take the citadel; it resulted in the Emir of Shaizar paying an indemnity and becoming the vassal of the Byzantine emperor. The forces of Zengi, the greatest Muslim prince of the region, skirmished with the allied army but it was too strong for them to risk battle. The campaign underlined the limited nature of Byzantine suzerainty over the northern Crusader states and the lack of common purpose between the Latin princes and the Byzantine emperor.

Having prepared his army for a renewed attack on Antioch, John amused himself by hunting wild boar on Mount Taurus in Cilicia, where he accidentally cut himself on the hand with a poisoned arrow. John initially ignored the wound and it became infected. He died a number of days after the accident, on 8 April 1143, probably of septicaemia. John's final action as emperor was to choose Manuel, the younger of his surviving sons, to be his successor. John is recorded as citing two main reasons for choosing Manuel over his older brother Isaac: Isaac's irascibility, and the courage that Manuel had shown on campaign at Neocaesarea. Another theory alleges that the reason for this choice was the AIMA prophecy, which foretold that John's successor should be one whose name began with an "M". Fittingly, John's close friend John Axouch, although he is recorded as having tried hard to persuade the dying emperor that Isaac was the better candidate to succeed, was instrumental in ensuring that Manuel's assumption of power was free from any overt opposition.

Overall, John II Komnenos left the empire a great deal better off than he had found it. Substantial territories had been recovered, and his successes against the invading Petchenegs, Serbs and Seljuk Turks, along with his attempts to establish Byzantine suzerainty over the Crusader States in Antioch and Edessa, did much to restore the reputation of his empire. His careful, methodical approach to warfare had protected the empire from the risk of sudden defeats, while his determination and skill had allowed him to rack up a long list of successful sieges and assaults against enemy strongholds. By the time of his death, he had earned near universal respect, even from the Crusaders, for his courage, dedication and piety.

Manuel I Komnenos was a Byzantine emperor of the 12th century who reigned over a crucial turning point in the history of Byzantium and the Mediterranean. His reign saw the last flowering of the Komnenian restoration, during which the Byzantine Empire had seen a resurgence of its military and economic power, and had enjoyed a cultural revival.

Eager to restore his empire to its past glories as the superpower of the Mediterranean world, Manuel pursued an energetic and ambitious foreign policy. In the process he made alliances with Pope Adrian IV and the resurgent West. He invaded the Norman Kingdom of Sicily, although unsuccessfully, being the last Eastern Roman emperor to attempt reconquests in the western Mediterranean. The passage of the potentially dangerous Second Crusade through his empire was adroitly managed. Manuel established a Byzantine protectorate over the Crusader states of Outremer. Facing Muslim advances in the Holy Land, he made common cause with the Kingdom of Jerusalem and participated in a combined invasion of Fatimid Egypt. Manuel reshaped the political maps of the Balkans and the eastern Mediterranean, placing the kingdoms of Hungary and Outremer under Byzantine hegemony and campaigning aggressively against his neighbours both in the west and in the east.

However, towards the end of his reign, Manuel's achievements in the east were compromised by a serious defeat at Myriokephalon, which in large part resulted from his arrogance in attacking a well-defended Seljuk position. Although the Byzantines recovered and Manuel concluded an advantageous peace with Sultan Kilij Arslan II, Myriokephalon proved to be the final, unsuccessful effort by the empire to recover the interior of Anatolia from the Turks.

Called ho Megas by the Greeks, Manuel is known to have inspired intense loyalty in those who served him. He also appears as the hero of a history written by his secretary, John Kinnamos, in which every virtue is attributed to him. Manuel, who was influenced by his contact with western Crusaders, enjoyed the reputation of "the most blessed emperor of Constantinople" in parts of the Latin world as well. Modern historians, however, have been less enthusiastic about him. Some of them assert that the great power he wielded was not his own personal achievement, but that of the dynasty he represented; they also argue that, since Byzantine imperial power declined catastrophically after Manuel's death, it is only natural to look for the causes of this decline in his reign.

In 1147 Manuel I granted a passage through his dominions to two armies of the Second Crusade under Conrad III of Germany and Louis VII of France. At this time, there were still members of the Byzantine court who remembered the passage of the First Crusade. The contemporary Byzantine historian Kinnamos describes a full-scale clash between a Byzantine force and part of Conrad's army, outside the walls of Constantinople. The Byzantines defeated the Germans and, in Byzantine eyes, this reverse caused Conrad to agree to have his army speedily ferried across to Damalis on the Asian shore of the Bosphoros. After 1147, however, the relations between the two leaders became friendlier. By 1148 Manuel had seen the wisdom of securing an alliance with Conrad, whose sister-in-law Bertha of Sulzbach he had earlier married; he actually persuaded the German king to renew their alliance against Roger II of Sicily. Unfortunately for the Byzantine emperor, Conrad died in 1152, and despite repeated attempts, Manuel could not reach an agreement with his successor, Frederick Barbarossa.

The Byzantine army soon advanced towards Antioch. Raynald knew that he had no hope of defeating the emperor, and in addition knew that he could not expect any aid from King Baldwin III of Jerusalem. Baldwin did not approve of Raynald's attack on Cyprus, and in any case had already made an agreement with Manuel. Thus isolated and abandoned by his allies, Raynald decided that abject submission was his only hope. He appeared dressed in a sack with a rope tied around his neck, and begged for forgiveness. Manuel at first ignored the prostrate Raynald, chatting with his courtiers. Eventually, Manuel forgave Raynald on condition that he would become a vassal of the Empire, effectively surrendering the independence of Antioch to Byzantium. Peace having been restored, a grand ceremonial procession was staged on 12 April 1159 for the triumphant entry of the Byzantine army into the city, with Manuel riding through the streets on horseback, while the Prince of Antioch and the King of Jerusalem followed on foot.

From the mid 11th century, the Kingdom of Hungary had been expanding its territory and influence southwards, with a view to annexing the regions of Dalmatia and Croatia. The Byzantines and Hungarians launched a number of invasions of each other's territory, and the Byzantines regularly aided pretenders to the Hungarian throne. Friction and outbreaks of open warfare between the Byzantines and Hungarians reached a peak in the 1150s and 1160s.

The Byzantine emperor Manuel I Komnenos attempted to achieve a diplomatic and dynastic settlement with the Kingdom of Hungary. In 1163, under the terms of an existing peace treaty, King Stephen III's younger brother Béla was sent to Constantinople to be raised under the personal tutelage of the emperor himself. As Manuel’s relative (Manuel's mother was a Hungarian princess) and the fiancé of his daughter, Béla became a Despotes (a title newly created for him) and in 1165 he was named as an heir to the throne, taking the name Alexios. But in 1167, King Stephen refused to give Manuel control of the former Byzantine territories allocated to Béla-Alexios as his appanage; this directly led to the war that ended with the Battle of Sirmium.

The Byzantines achieved a decisive victory, forcing the Hungarians to sue for peace on Byzantine terms. They also agreed to provide hostages for good behaviour; to pay Byzantium a tribute and supply troops when requested. The Battle of Sirmium completed Manuel's drive to secure his northern frontier.

In the autumn of 1169 Manuel sent a joint expedition with Amalric to Egypt: a Byzantine army and a naval force of 20 large warships, 150 galleys, and 60 transports joined forces with Amalric at Ascalon. The joined forces of Manuel and Amalric laid siege to Damietta on 27 October 1169, but the siege was unsuccessful due to the failure of the Crusaders and the Byzantines to co-operate fully. When the rains came, both the Latin army and the Byzantine fleet returned home, although half of the Byzantine fleet was lost in a sudden storm.

The Battle of Myriokephalon was a battle between the Byzantine Empire and the Seljuk Turks in Phrygia in the vicinity of Lake Beyşehir in southwestern Turkey on 17 September 1176. The battle was a strategic reverse for the Byzantine forces, who were ambushed when moving through a mountain pass. It was to be the final, unsuccessful effort by the Byzantines to recover the interior of Anatolia from the Seljuk Turks.

From the late 11th century, Western merchants, primarily from the Italian city-states of Venice, Genoa and Pisa, had started appearing in the East. The first had been the Venetians, who had secured large-scale trading concessions from Byzantine emperor Alexios I Komnenos. Subsequent extensions of these privileges and Byzantium's own naval impotence at the time resulted in a virtual maritime monopoly and stranglehold over the Empire by the Venetians.

Alexios' grandson, Manuel I Komnenos, wishing to reduce their influence, began to reduce the privileges of Venice while concluding agreements with her rivals: Pisa, Genoa and Amalfi. Gradually, all four Italian cities were also allowed to establish their own quarters in the northern part of Constantinople itself, towards the Golden Horn.

Following the death of Manuel I in 1180, his widow, the Latin princess Maria of Antioch, acted as regent to her infant son Alexios II Komnenos. Her regency was notorious for the favoritism shown to Latin merchants and the big aristocratic land-owners, and was overthrown in April 1182 by Andronikos I Komnenos, who entered the city in a wave of popular support. Almost immediately, the celebrations spilled over into violence towards the hated Latins, and after entering the city's Latin quarter a mob began attacking the inhabitants.

Many had anticipated the events and escaped by sea. The ensuing massacre was indiscriminate: neither women nor children were spared, and Latin patients lying in hospital beds were murdered. Houses, churches, and charities were looted. Latin clergymen received special attention, and Cardinal John, the papal legate, was beheaded and his head was dragged through the streets at the tail of a dog.

Although precise numbers are unavailable, the bulk of the Latin community, estimated at 60,000 at the time by Eustathius of Thessalonica, was wiped out or forced to flee. The Genoese and Pisan communities especially were devastated, and some 4,000 survivors were sold as slaves to the (Turkish) Sultanate of Rum. The massacre further worsened relations and increased enmity between the Western and Eastern Christian churches, and a sequence of hostilities between the two followed.

Manuel's death on 24 September 1180, marked a turning point in the fortunes of the Byzantine Empire. Andronikos began his reign well. in particular, the measures he took to reform the government of the empire have been praised by historians. In the provinces, Andronikos' reforms produced a speedy and marked improvement. Andronikos's fierce determination to root out corruption and many other abuses was admirable; under Andronikos, the sale of offices ceased; selection was based on merit, rather than favouritism; officials were paid an adequate salary so as to reduce the temptation of bribery. Every form of corruption was eliminated with ferocious zeal.

There were several revolts, leading to an invasion by King William II of Sicily. Andronikos hastily assembled five different armies to stop the Sicilian army from reaching Constantinople, but his forces failed to stand and retreated to the outlying hills. Andronikos also assembled a fleet of 100 ships to stop the Norman fleet from entering the Sea of Marmara.

When Andronikos returned to Constantinople, he found that his authority was overthrown: Isaac Angelos had been proclaimed emperor. The deposed Emperor attempted to escape in a boat with his wife Agnes and his mistress, but was captured. Isaac handed him over to the city mob and for three days he was exposed to their fury and resentment. His right hand was cut off, his teeth and hair were pulled out, one of his eyes was gouged out, and, among many other sufferings, boiling water was thrown in his face. He died on September 12, 1185. At the news of the emperor's death, his son and co-emperor, John, was murdered by his own troops in Thrace.

Isaac Doukas Komnenos was a claimant to the Byzantine Empire and the ruler of Cyprus from 1184 to 1191. Contemporary sources commonly call him the emperor of Cyprus. He lost the island to King Richard I of England during the Third Crusade.

It was during the Komnenian period that contact between Byzantium and the 'Latin' Christian West, including the Crusader states, was at its most crucial stage. Venetian and other Italian traders became resident in Constantinople and the empire in large numbers, and their presence together with the numerous Latin mercenaries who were employed by Manuel in particular helped to spread Byzantine technology, art, literature and culture throughout the Roman Catholic west. Above all, the cultural impact of Byzantine art on the west at this period was enormous and of long lasting significance. The Komnenoi also made a significant contribution to the history of Asia Minor. By reconquering much of the region, the Komnenoi set back the advance of the Turks in Anatolia by more than two centuries.;

The Komnenian period was followed by the dynasty of the Angeloi, who oversaw perhaps the most crucial period in the Decline of the Byzantine Empire. The next quarter of a century would see Constantinople fall to an invading force for the first time in its history, and the final loss of the empire's 'great power' status. However, with the death of Andronikos, the Komnenian dynasty, having lasted 104 years, had finally come to an end.