The Diocese of Tortona is a Latin Church ecclesiastical territory or diocese of the Catholic Church in Northern Italy, spanning parts of three regions of Piedmont, Lombardy and Liguria. It is a suffragan diocese in the ecclesiastical province of the metropolitan Archdiocese of Genoa and forms part of the ecclesiastical region of Liguria. The diocese claims to be one of the oldest in Lombardy and the Piedmont.

The naval Battle of Giglio was a military clash between a fleet of the Holy Roman Emperor Frederick II and a fleet of the Republic of Genoa in the Tyrrhenian Sea. It took place on Friday, May 3, 1241 between the islands of Montecristo and Giglio in the Tuscan Archipelago and ended with the victory of the Imperial fleet.