The first urban centre was created around 800 BC., when the inhabitants of small scattered villages gathered together and founded the first organized settlement. This new town of the late geometric period was located in Agios Stefanos Bay, which became the town harbour and a centre of navigation and commerce. Metalwork and pottery developed. At the same time an intense movement of colonization is observed to the North (Macedonia, Thrace) and the West (Italy, Sicily) is observed.Up to 600 A.D., that is, for fourteen centuries, Chalcis flourished and declined at the same location around Agios Stefanos Bay. The effort of the Department of Antiquities of Euboea undertaken at the moment is to determine the successive phases of the town planning development and organization of ancient Chalcis. The decade 610-620 A.D., when the ancient town is abandoned and transferred to a neighboring location on the hill dominating the Euripus strait, is considered a crucial historic landmark. The new, small town l fortress, the “Castle”, is fortified and thus a suitable harbour for the royal ships is secured. It is suggested that the transfer and the fortification of coastal towns such as Chalkis, Monemvasia, Corfu etc. belonged to a broader defense plan of the Byzantine Empire, attributed to the Emperor Herakleios (610-641 A.D.). This plan aimed at control of the sea, a goal to be achieved through the reorganization of the royal navy and the resistance against the Abars and the Slavs. Fortified harbours ensured the inhabitants’ safety and made possible the mooring and supplying of the fleetwith provisions The new choice of position proved successful and the new fortified town of Chalcis became in the Middle Ages known throughout the east Mediterranean Sea as the “Castle of Euripus”.