In 1571, a Christian fleet, led by Philip's half-brother John of Austria, annihilated the Ottoman fleet at the Battle of Lepanto in the waters off southwestern Greece. Despite the significant victory, however, the Holy League's disunity prevented the victors from capitalizing on their triumph. Plans to seize the Dardanelles as a step towards recovering Constantinople for Christendom, were ruined by bickering amongst the allies. With a massive effort, the Ottoman Empire rebuilt its navy. Within six months a new fleet was able to reassert Ottoman naval supremacy in the eastern Mediterranean. John captured Tunis (in present-day Tunisia) from the Ottomans in 1573, but it was soon lost again. The Ottoman sultan agreed to a truce in the Mediterranean with Philip in 1580. In the western Mediterranean, Philip pursued a defensive policy with the construction of a series of military forts (presidios) and peace agreements with some of the Muslim rulers of North Africa.