Euboea, or Negropont or Negroponte is the second largest of the Greek Aegean Islands and the second largest Greek island overall in area (1609 sq. miles) and population (after Crete). It is separated from the mainland of Greece by the Euboic Sea. In general outline it is a long and narrow, seahorse-shaped island; it is about 150 km (90 miles) long, and varies in breadth from 50 km (30 miles) to 6 km (4 mi). Its general direction is from N.W. to S.E., and it is traversed throughout its length by a mountain range, which forms part of the chain that bounds Thessaly on the east, and is continued south of Euboea in the lofty islands of Andros, Tenos, and Mykonos.

Euboea was believed to have originally formed part of the mainland, and to have been separated from it by an earthquake. This is fairly probable, because it lies in the neighbourhood of a fault line, and both Thucydides and Strabo write that the northern part of the island had been shaken at different periods. Its northern extremity is separated from the Thessalian coast by a strait, which at one point is not more than 130 feet (40 metres) wide (see satellite photo [1] ). In the neighbourhood of Chalcis, both to the north and the south, the bays are so confined as to make plausible the story of Agamemnon's fleet having been detained there by contrary winds. At Chalcis itself, where the strait is narrowest, it is called the Euripus. The extraordinary changes of tide which take place in this passage have been a subject of note since classical times. At one moment the current runs like a river in one direction, and shortly afterwards with equal velocity in the other. A bridge was first constructed here in the twenty-first year of the Peloponnesian War (410 BC). The name Euripus was corrupted during the Middle Ages into Evripo and Egripo, and in this latter form transferred to the whole island. Later the Venetians, when they occupied the district, altered it to Negroponte, referring to the bridge which connected it with the mainland.

Like most of the Greek islands, Euboea was originally known under other names, such as Macris and Doliche from its shape, and Ellopia and Abantis (Άβαντες) from the tribes inhabiting it.

The main mountains include Dirphys (1,745 m), Pyxaria (1,341 m) in the northeast and Ochi (1,394).

The neighboring gulfs are the Pagasetic Gulf in the north, Maliakos Gulf, Northern Euboean Gulf in the west, the Euboic Sea and the Petalion Gulf.