The Byzantine–Norman wars were a series of military conflicts between the Normans and the Byzantine Empire fought from c. 1040 to 1186 involving the Norman-led Kingdom of Sicily in the west, and the Principality of Antioch in the Levant.

Eventually, some Normans, including the powerful de Hauteville brothers, served in the army of George Maniakes during the attempted Byzantine reconquest of Sicily, only to turn against their employers when the emirs proved difficult to conquer.

[4] When Alexios I Comnenus ascended to the throne of Byzantium, his early emergency reforms, such as requisitioning Church money—a previously unthinkable move—proved too little to stop the Normans.

He enhanced this by bribing the German king Henry IV with 360,000 gold pieces to attack the Normans in Italy, which forced Guiscard to concentrate on his defenses at home in 1083–1084.

This forced Bohemond to retreat to Epirus and Alexios was able to recover Castoria and convince many Normans, including Peter Aliphas, to enter his services.

[11] Out of fear that this signaled Byzantine intentions to reconquer southern Italy and remove his suzerainty over the Normans, Pope Innocent II declared the emperor an excommunicate, and threatened any Latin Christian who served in his army with the same consequence.

However, despite being distracted by a Cuman attack in the Balkans, in 1148 Manuel enlisted the alliance of Conrad III of Germany, and the help of the Venetians, who quickly defeated Roger with their powerful fleet.

[14] In 1149, Manuel recovered Corfu and prepared to take the offensive against the Normans, while Roger II sent George of Antioch with a fleet of 40 ships to pillage Constantinople's suburbs.

The renewal of the German alliance remained the principal orientation of Manuel's foreign policy for the rest of his reign, despite the gradual divergence of interests between the two empires after Conrad's death.

[14] The death of Roger in February 1154, who was succeeded by William I, combined with the widespread rebellions against the rule of the new King in Sicily and Apulia, the presence of Apulian refugees at the Byzantine court, and Frederick Barbarossa's (Conrad's successor) failure to deal with the Normans encouraged Manuel to take advantage of the multiple instabilities that existed in the Italian peninsula.

[b] Nevertheless, with the help of disaffected local barons including Count Robert of Loritello, Manuel's expedition achieved astonishingly rapid progress as the whole of southern Italy rose up in rebellion against the Sicilian Crown, and the untried William I.

[25] In the aftermath of the fall of Andronikos, a reinforced Byzantine field army under Alexios Branas decisively defeated the Normans at the Battle of Demetritzes.

The exception was the County palatine of Cephalonia and Zakynthos, which remained in the hands of the Norman admiral Margaritus of Brindisi and his successors until it fell to the Turks in 1479.

[26] The successive Sicilian rulers would eventually continue the Norman policy of domination over post-Byzantine states in the Ionian Sea and Greece, attempting to assert suzerainty over Corfu, finally conquered in 1260, the County palatine of Cephalonia and Zakynthos, the Despotate of Epirus and other territories.