The ruins of an important settlement of the Classical and Hellenistic periods lie on Kastri hill, north of the village of Potamia, in Euboea. Surface finds from the southern slopes of the hill indicate that the site was inhabited from the Neolithic period (fourth millennium BC) onwards.
The Classical town was founded in the fourth century BC and is believed to have remained under the control of Eretria until the third century BC. A strong fortification wall surrounded the city, and archaeological finds suggest a number of industrial activities. Archaeological finds include a metallurgy furnace, roof tiles, clay loom weights, terracotta figurines, fragmentary grinding stones, bronze coins, small metal objects, stone tesserae, inscribed tiles, stones with painted undeciphered signs or letters, and a large number of bronze coins. Most of the coins are third century BC mints of the Euboean League, the most common numismatic type having a bull on the obverse and a grape-bunch on the reverse. The remaining coins come from Chalkis, Istiaia, Eretria, Athens, Chios, and Macedonia, and date from the third and second centuries BC. The Macedonian coins date from the period of Antigonos Gonatas (277-239 BC) and bear the head of Athena on the obverse and the god Pan holding a trophy on the reverse. The hill was inhabited until the early first century BC, and there is no archaeological evidence for building activity or occupation until the sixth century AD. Sparse architectural remains of the sixth century AD suggest that the fortified site of Kastri may have served as an observation post during the Early Byzantine period and later.
Surface investigations at Kastri began in the early twentienth century by K. Papaioannou, schoolteacher at Kymi and Curator of Antiquities, and were continued by G. Papavasileiou, high-school principal at Chalkis. The archaeologist A. Sampson excavated the site in 1976-1978 with funds made available by the Municipality of Kymi and the Community of Potamia.