The Gulf of Euboea, Euboean Gulf, Euboic Sea or Euboic Gulf (modern Greek: Ευβοϊκός Κόλπος, Evvoïkós Kólpos) is an arm of the Aegean Sea between the island of Euboea (northeast coastline) and the Greek mainland (southwest coastline). Trending diagonally northwest-southeast, the gulf is divided by the narrow Strait of Euripus, at the town of Chalcis (Khalkís). The North Euboean Gulf is about 50 miles (80 km) long and up to 15 miles (24 km) wide, and the South Euboean Gulf is about 30 miles (48 km) long, with a maximum width of 9 miles (14 km).