The Euripus Strait ( ) is a narrow channel of water separating the Greek island of Euboea in the Aegean Sea from Boeotia in mainland Greece. The strait's principal port is Chalcis on Euboea, located at the strait's narrowest point. The strait is subject to strong tidal currents which reverse direction approximately four times a day. Tidal flows are very weak in the Eastern Mediterranean, but the strait is a remarkable exception. Water flow peaks at about , either northwards or southwards, and lesser vessels are often incapable of sailing against it. When nearing flow reversal, sailing is even more precarious because of vortex formation. The Swiss scholar François-Alphonse Forel contributed to an understanding of the enigmatic phenomenon by his study of limnology and the discovery of seiche, where layers of water of differing temperature oscillate in thickness in a confined body of water. But the problem was solved completely only by D. Eginitis, director of the Athens Observatory, who published his conclusions in 1929. Etymology From Ancient Greek (eúrīpos, "any strait or narrow sea, where the flux and reflux is violent"); from (eû, "well") + (rhipḗ, “swing or force with which anything is thrown”), from (rhíptō, "to throw"). Bridges There are two road bridges across the strait, both at Chalcis. One is the Euripus Bridge or Chalcis Bridge, a two-pylon, cable-suspended bridge built south of town in 1992, and commonly called the "New" or "High" bridge, with a span of about 215 m (705 ft). The strait is 160 m (525 ft) wide at this point. The bridge is accessible via a fork on the main road at Aulis. The "Old" or "Low" or "Sliding" Bridge lies across midtown, and can slide away to allow shipping traffic. It is located at the narrowest point of the strait, where it is only 38 m (125 ft) wide. It accommodates two lanes of vehicular traffic. It was originally built as a retractable bridge in 1858, replaced by a rotating one in 1896. The existing, originally wooden bridge was built in 1962 and was extensively refurbished in 1998. History The Euripus was closed by a dike of coarse sediment until about 6000 years ago, when it was opened by an (unrecorded) earthquake. Herodotus mentions the strait during his description of the Battle of Artemisium (480 BC), with the account implying that it was navigable by large fleets of triremes. Diodorus Siculus reports