Alexios I Komnenos, newly crowned Emperor in Constantinople, dispatches an urgent message to Doge Domenico Selvo asking for the mobilization of the Venetian fleet in defense of Durazzo in return for great rewards.
The Doge wastes no time in setting sail for the besieged city in charge of his fleet of fourteen warships and forty-five other vessels.
Selvo, feeling his polity equally threatened, himself commands the fleet.
Selvo is motivated not only by his familial ties and the promise of reward, but also the realization that Norman control over the Strait of Otranto would be just as great of a threat to Venetian power in the region as it would be to their ally in the east.
Robert's ships are hit by a sudden tempest, and several ships are lost; a Venetian fleet now appears on the northwestern horizon.
The Venetians hoist dinghies to the yardarms from which they shoot arrows and use Greek fire against the inexperienced Norman seamen, who are mostly used to land battle.
The battered fleet led by Guiscard retreats into the harbor after losing many ships.
The defeat, though devastating to Guiscard's fleet, has inflicted little damage to his army as the majority of it has disembarked before the battle in preparation of the siege of Dyrrhachium, which will continue throughout the summer.
Selvo, victorious at sea, leaves the fleet under the command of his son and returns to Venice a hero.
Nikephoros Melissenos, the former pretender to the throne, commands the imperial army's right wing, marches alongside Alexios, who arrives in October with his army.
His Varangian Guard now consists largely of Englishmen, Anglo-Saxons who had left their country in disgust after Hastings (1066) and have taken service with Constantinople.
Many of them have been waiting fifteen years for an opportunity to avenge the Norman Conquest, and they attack with all the vigor of which they are capable.
Swinging their huge two-handed battle-axes around their heads and then slamming them into horses and riders, they inspire terror among the Apulian knights, few of whom have ever come across a line of foot-soldiers that had not immediately broken in the face of a cavalry charge.
The horses begin to panic also, and the Norman right soon turns in confusion, with many galloping into the sea to escape.
Sikelgaita, reputedly a Valkyrie of immense build and Herculean physical strength, rides after the Normans and threatens to impale them with her spear.
Thus rallied, they recover and return to the fray.
The Norman left, under Bohémond's command, wheels to the rescue with a detachment of crossbowmen against whom the Varangians, unable to approach within ax range, find themselves defenseless.
The Varangians retreat to a chapel that the Normans immediately burn down; most perish.
