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 Dokeianos, the Byzantine Catepan of Italy. Suffering heavy losses in the battle, the Byzantines were eventually defeated, and the remaining forces retreated to Bari. Dokeianos 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.

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.

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.

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