An attack on the North African town of Mahdia by armed ships from Genoa and Pisa in northern Italy is prompted by the actions of its ruler Tamim ibn Muizz as a pirate in waters off the Italian peninsula, along with his involvement in Sicily fighting the Norman invasion.

The attack is led by Hugh of Pisa, with military aid from Rome; the nobleman Pantaleone from Amalfi is also involved, and the whole endeavor has the backing of Countess Matilda of Tuscany.

The attackers succeed in capturing the city, but they cannot hold it; the money from the plunder is spent on the cathedral at Pisa and to build a new church.

The attack plays a critical role in the Christians' seizure of control of the Western Mediterranean, which will allow the First Crusade to be supplied by sea.