Battle of Montemaggiore The Battle of Montemaggiore ( or Monte Maggiore ) was fought on 4 May 1041 , on the river Ofanto near Cannae in Byzantine Italy , between Lombard - Norman rebel forces and the Byzantine Empire . The Norman William Iron Arm led the offence , which was part of a greater revolt , against Michael Doukeianos , the Byzantine Catepan of Italy . Suffering heavy losses in the battle , the Byzantines were eventually defeated , and the remaining forces retreated to Bari . Doukeianos was replaced and transferred to Sicily as a result of the battle . The victory provided the Normans with increasing amounts of resources , as well as a renewed surge of knights joining the rebellion . Background . The battle was fought on 4 May 1041 , less than two months after the Battle of Olivento , the first battle of a renewed revolt of Lombard - Norman forces against the Byzantine Empire instigated by Arduin the Lombard . The battle at Olivento was the first battle between Normans and Byzantines since the Battle of Cannae in 1018 , but the outcome shifted this time from Byzantine victory to defeat . While the Normans originally only fought as mercenaries in Italy , they took increasing control during the 1041 revolt , and started to carve out territory for themselves after the Battle of Montemaggiore . The site of the battle was the river Ofanto near Cannae , but the name of the mountain Montemaggiore is usually used to refer to the 1041 battle . Battle . The Norman offence at Montemaggiore was led by William Iron Arm , who was elected the leader of the Normans . Also present were William ' s two younger brothers , Drogo and Humphrey . The Norman contingent gained considerable strength following the previous battle at Olivento , as new Lombard auxiliaries and Norman mercenaries from Salerno and Aversa , led by Rainulf Drengot , bolstered their ranks . The Lombard - Norman army is said to have included 2 , 000 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 700 Norman knights and about 1 , 300 foot soldiers , roughly double the number estimated by Gordon S . Brown for the preceding battle , in Olivento . The Byzantine catepan , Michael Doukeianos , met the Normans with a numerically greater army . His army is claimed to have included 18 , 000 men in the Bari Annals ( " Annales barenses " ) , but estimated by Brown as " several thousand " ( at Olivento ) . The army was divided into two lines , and consisted of fresh troops from Asia and returning soldiers from Sicily . The Byzantine forces also included the Norse - dominated Varangian Guard , led by the future Norwegian king Harald Hardrada , and was morally bolstered by the presence of two Greek Rite bishops from Troia and Ofanto . The Normans attacked the Byzantines in a spearhead formation , which led the first line to be driven into the second , and in turn causing confusion among the Byzantines . William suffered from fever and initially watched the fight from a hill , but eventually joined the battle as he was overcome with excitement . A great number of Byzantine soldiers , including the two bishops , drowned in the Ofanto attempting to flee . A particularly great number of Varangians also fell in battle , and the Byzantines were eventually defeated in the battle . The Norman victory has been attributed in particular to the addition of the Norman heavy cavalry . Aftermath . With the Byzantine army crushed , Michael Doukeianos fell back to the port of Bari , requesting new reinforcements from Sicily . Instead , Doukeianos was transferred to Sicily and replaced by Exaugustus Boioannes . The victory at Montemaggiore provided 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 attracted more knights to join the rebellion . The 1041 Lombard - Norman revolt was followed by a third and final battle , the Battle of Montepeloso in September .