The Battle of Lepanto was the last great galley naval battle fought in the Mediterranean Sea. It took place on the 6th and 7th October 1571, between Don Juan of Austria and the Ottoman empire. The battle was decisive in keeping Europe Christian out of the hands of the Muslim Turks.
Tradition has it that the sailors prayed the Rosary on the eve of battle and in order to commemorate this fact and in thanksgiving for victory Pope Pius V inaugurated this feast. Today's feast calls on us all to remember the mysteries of Christ as laid down in the Rosary and to remember the power of this prayer in seeking the intervention of Christ in our lives. The scale of the victory at sea is a pale reflection of the scale of Christ's victory over death and the promise of the Resurrection for us as Christians.
The great English convert, G.K. Chesterton wrote a poem "Lepanto" about the battle in which he speaks openly of the intercession of Mary on behalf of the Christians.