It was on this day in 1571 that a massive Turkish battle fleet was stunningly defeated by a Christian coalition called the Holy League made up of the combined forces of the Kingdom of Spain, the Duchy of Savoy, the Papal States, the Republic of Venice, the Republic of Genoa and the Knights of Malta though many of the soldiers on board the fleet came from an even wider array of nations from Germany to Croatia. It was the first time in about a hundred years that the Ottoman Turks had been defeated at sea and was a crushing blow to the morale of the Ottoman Empire. The Christian forces were led by the swashbuckling romantic Don Juan of Austria, son of the Holy Roman Emperor Charles V and half-brother of King Philip II of Spain. The Turks were banking on their record of success and overwhelming force. The Christians had better ships and superior weaponry.
This was no minor engagement but possibly the most pivotal naval battle since Actium. The Turks had vowed to invade Italy, conquer Rome and convert St Peter's Basilica into a mosque. This was no empty threat. The Ottoman forces had been advancing on every front and seemed everywhere unbeatable. That was probably their greatest advantage; that recent history had caused many to believe the Ottoman Empire to be impossible to defeat. The Sultan had given his naval commander Ali Pasha the famous "Banner of the Caliphs" to encourage his men as they sailed into battle. The Christians had their own blessed banners as well and Pope St Pius V called on all Catholics to pray the rosary for victory. When the victory at Lepanto was won it was credited to the miraculous intervention of the Blessed Virgin Mary and the Pope commemorated the event with the Feast of Our Lady of Victory, later the Feast of Our Lady of the Rosary. Adding to the collapse of morale for the Ottoman forces, their commander was killed in battle and the prized Banner of the Caliphs captured.
The victory was crucial for the Catholic powers of southern Europe (the Protestant Christian nations were cheering the Turks in most cases) but it was not so terrible a loss for the Turks in concrete terms. They had taken Cyprus and soon had a respectable fleet built back up again, yet they would never again dominate the Mediterranean Sea and squabbling among the Christians prevented them from re-taking Constantinople as the Pope had intended. The Turks were still the single most powerful empire around but they had lost their seemingly invincible status was lost. In the years and centuries that followed it would be the Christian powers that expanded and the Muslim powers that fell back.