narrow strait in the Aegean Sea (an arm of the Mediterranean Sea), between the Greek island of Euboea (Évvoia) and the mainland of central Greece. It is 5 miles (8 km) long and varies from 130 feet (40 m) to 1 mile (1.6 km) in width. It has strong tidal currents (often reaching velocities of 12 knots) that reverse directions seven or more times a day. According to popular tradition, the ancient Greek philosopher Aristotle, in despair at his inability to solve the problem of their cause, drowned here; their cause is not fully understood today. The main port on the strait is Chalcis, or Khalkís (Euboea), an important trading centre since the times of ancient Greece. A 130-foot (40-metre) movable bridge spans the strait at Chalcis, replacing earlier structures that dated back to 411 BC.