From the heights of Gibraltar you can see Africa about nine miles to the south and gaze eastward on the seemingly endless Mediterranean that stretches 1,500 miles to Asia beyond. The Romans called it Mare Nostrum, "our sea," and these deep blue waters allowed Rome to unite Asia, Africa, and Europe for half a millennium under a single prosperous, globalized civilization. But the Mediterranean has not always proved to be history's incubator of great civilizations -- Greek, Roman, Byzantine, Ottoman, Florentine, and Venetian. Sometimes the ancient "Pillars of Hercules" at Gibraltar's narrow mouth of the Mediterranean marked not so much...
