The Battle of Dyrrhachium took place on October 18, 1081 between the Byzantine Empire, led by the Emperor Alexios I Komnenos (r. 1081–1118), and the Normans of southern Italy under Robert Guiscard, Duke of Apulia and Calabria.

The battle was fought outside the city of Dyrrhachium (present-day Durrës in Albania), the major Byzantine stronghold in the western Balkans, and ended in a Norman victory.

Robert was then forced to leave Greece to deal with an attack on his ally, the Pope, by the Holy Roman Emperor, Henry IV (r. 1084–1105).

The Normans first arrived in Southern Italy in 1015 from northern France and served local Lombard lords as mercenaries against the Byzantine Empire.

[7] In 1059, Pope Nicholas II made Robert Guiscard, of the Hauteville family, Duke of Apulia, Calabria, and Sicily.

[10] This gave Robert a pretext to invade the empire claiming his daughter had been mistreated; however, his intervention was delayed by a revolt in Italy.

[12] Meanwhile, he sent an ambassador to the Byzantine court with orders to demand proper treatment for Helena and to win over the Domestic of the Schools, Alexios.

When the ambassador returned, he urged Robert to make peace, claiming that Alexios wanted nothing but friendship with the Normans.

From all quarters of Lombardy and Apulia he gathered them, over age and under age, pitiable objects who had never seen armour in their dreams, but then clad in breastplates and carrying shields, awkwardly drawing bows to which they were completely unused and following flat on the ground when they were allowed to march...Yet, however unused to soldiering they were, he (Robert Guiscard) trained them daily and hammered his recruits into a disciplined force.

Having won a bridgehead and a clear path for reinforcements from Italy, he advanced on the city of Dyrrhachium, the capital and chief port of Illyria.

[16] Meanwhile, when Alexios heard that the Normans were preparing to invade Byzantine territory, he sent an ambassador to the Doge of Venice, Domenico Selvo, requesting aid and offering trading rights in return.

The Byzantine garrison at Dyrrhachium managed to hold out all summer, despite Robert's catapults, ballistae and siege tower.

[20] Robert's camp was struck by disease; according to contemporary historian Anna Comnena up to 10,000 men died, including 500 knights.

Alexios also withdrew the tagmas from Heraclea Pontica and the remaining Byzantine holdings in Asia Minor and by doing so, he effectively left them undefended.

[22] He held a war council there and sought advice from his senior officers; among them was George Palaiologos, who had managed to sneak out of the city.

[23] Guiscard, however, had been informed of Alexios' arrival by his scouts and on the night of October 17, he moved his army from the peninsula to the mainland.

The Varangians stood their ground while the Byzantine left, including some of Alexios' elite troops, attacked the Normans.

Alexios's ally, Serbian King Constantine Bodin stayed aside with his army, intending to await the outcome of the battle.

While escaping, he was wounded in his forehead and lost a lot of blood, but eventually made it back to Ohrid, where he regrouped his army.

[24] "Alexios was undoubtedly a good tactician, but he was badly let down by the undisciplined rush to pursue the beaten enemy wings, a cardinal sin in the Byzantine tactical manuals.

[4] Historian Robert Holmes states: "The new knightly tactic of charging with the lance couched – tucked firmly under the arm to unite the impact of man and horse – proved a battle-winner.

While Guiscard was in Kastoria, messengers arrived from Italy, bearing news that Apulia, Calabria, and Campania were in revolt.

He also learned that the Holy Roman Emperor, Henry IV, was at the gates of Rome and besieging Pope Gregory VII, a Norman ally.

[36] Meanwhile, Alexios granted the Venetians a commercial colony in Constantinople, as well as exemption from trading duties in return for their renewed aid.