The Battle of Lepanto was a naval engagement that took place on 7 October 1571 when a fleet of the Holy League, a coalition of Catholic states (comprising Spain and most of Italy) arranged by Pope Pius V, inflicted a major defeat on the fleet of the Ottoman Empire in the Gulf of Patras. The Ottoman forces were sailing westward from their naval station in Lepanto (the Venetian name of ancient Naupactus) when they met the fleet of the Holy League which was sailing east from Messina, Sicily. The Spanish Empire and the Venetian Republic were the main powers of the coalition, as the league was largely financed by Philip II of Spain, and Venice was the main contributor of ships.

The victory of the Holy League is of great importance in the history of Europe and of the Ottoman Empire, marking the turning-point of Ottoman military expansion into the Mediterranean, although the Ottoman wars in Europe would continue for another century. It has long been compared to the Battle of Salamis, both for tactical parallels and for its crucial importance in the defense of Europe against imperial expansion. It was also of great symbolic importance in a period when Europe was torn by its own wars of religion following the Protestant Reformation. Pope Pius V instituted the feast of Our Lady of Victory, and Philip II of Spain used the victory to strengthen his position as the "Most Catholic King" and defender of Christendom against Muslim incursion.