The Bosporus Strait ebbs and flows through the heart of Istanbul, its presence lending the city an added vitality. As the only means of passage between the Sea of Marmara and the Black Sea and a gateway for trade to the Aegean and Mediterranean seas, the 31-kilometer (19-mile) strait has been the lifeline for Istanbul since ancient gods ruled the Earth. According to Greek mythology, the Bosporus was born of a legend involving Zeus, his lover Io, and Zeus’s vengeful wife, Hera. To hide his affair from Hera, Zeus turned Io into a white cow, but Hera, aware of the deception, sent a horsefly to sting the cow. The pain sent Io racing across the Bosporus, or “the passage of the cows” in the ancient Thracian language of the region. These days, the gods look on from above as passengers aboard modern-day cruise liners, cargo ships and commuter ferries sail along and across the Bosporus, stirring both the vestiges of Istanbul’s past and the strait’s modern vibe as one of the world’s busiest shipping and transportation routes, one that divides Europe and Asia.