The island of Euboea, the largest of the Greek islands after Crete, extends over almost 175 km parallel to continental Greece, from which it is separated only by a narrow channel: the Euripos. At the narrowest point in the strait, the island is connected with the continent by a bridge that crosses the sea near the city of Chalkis.
The breadth of the island varies considerably, ranging from about 20 km near Chalkis to less than 3 km in the Styra region. Its morphology is varied and pronounced. A dozen peaks rise to altitudes between 1,000 and 1,450 m, of which Mount Dirphys is the highest at 1,745 m.
The lowlands lie mainly along the coasts, and include the Lelantine plain and the plains of Aliverion, Politika-Psachna and Histiaea. These fertile regions are often conditioned by the large alluvial fans of seasonal watercourses.
Eretria between sea and land
Eretria is located west of the plain of Amarynthos on the south coast of the island. The Olympos range runs north of it and turns south to meet the sea, thus creating a lowland surrounded by a mountain barrier.
The plain is dominated by Mount Voudochi (797 m), whose steep slopes are cut by numerous thalwegs and serve as watersheds. As a result of intense erosion, large quantities of calcareous materials are torn from the mountain and carried down to the foot of the massif, where the largest blocks accumulate in stone fields (alluvial fans); sand and gravel are carried further on by small watercourses. The gently sloping terrain allows the finest sediments to be deposited, thus creating soils suitable for cultivation.
The rainwater is then collected and drained away by a river that leads toward the sea. Before humans put their mark on the site of Eretria, this river, which was probably dry during the summer months, spread out into a delta, creating along the coast a wet and sometimes marshy land, crossed by several branches that flowed into the sea. As a result, the coastline has constantly evolved, sometimes affected by variations in the sea level, sometimes by additional alluvial deposits carried down by the river, until it formed a natural port to which humans later gave the shape it has today.
The other distinctive feature of the Eretrian landscape is a calcareous outcropping that rises a few hundred meters from the coast: the acropolis, 123 m in altitude, which dominates the river delta. From its summit, one looks out toward the south on the Euboean channel, the coast of Boeotia and Attica, and toward the north at the imposing Olympos range.