The Norman offensive at Montemaggiore is led by William Iron Arm, who has been elected the leader of the Normans.

Also present are William's two younger brothers, Drogo and Humphrey.

The Norman contingent had gained considerable strength following the previous battle at Olivento, as new Lombard auxiliaries and Norman mercenaries from Salerno and Aversa, led by Rainulf Drengot, have bolstered their ranks.

The Lombard-Norman army is said to have included two thousand Norman knights, considered an inflated number by modern historians, in addition to Lombard infantry and heavy cavalry formations.

Historian Richard Humble has put the army's numbers at seven hundred Norman knights and about thirteen hundred foot soldiers, roughly double the number estimated by Gordon S. Brown for the preceding battle, in Olivento.

The imperial catepan, Michael Doukeianos, meets the Normans with a numerically greater army.

His army is claimed to have included eighteen thousand men in the Bari Annals (Annales barenses), but estimated by Brown as "several thousand" (at Olivento).

The army is divided into two lines, and consists of fresh troops from Asia and returning soldiers from Sicily.

The imperial forces also include the Norse-dominated Varangian Guard, led by the future Norwegian king Harald Hardrada, and is morally bolstered by the presence of two Greek Rite bishops from Troia and Ofanto.

The Normans attack the imperial army in a spearhead formation, which leads the first line to be driven into the second, and in turn causing confusion among the Greeks.

William suffers from fever and initially watches the fight from a hill, but eventually joins the battle as he is overcome with excitement.

A great number of imperial soldiers, including the two bishops, drown in the Ofanto attempting to flee.

A particularly great number of Varangians also fall in battle, and the imperial troops are eventually defeated.

The Norman victory has been attributed in particular to the addition of the Norman heavy cavalry.

The victory at Montemaggiore provides the Normans with their first significant acquisition of war booty, including military equipment, horses, tents, precious fabrics, as well as gold and silver vessels.

The enrichment of the soldiers in turn attracts more knights to join the rebellion.

With the imperial army crushed, …