The arched building in Posidi, is one of the most ancient sanctuaries in Greece and the unique with the building of the Dark Centuries for worship use from North Greece. The results of the excavations in the ancient Mendi were considered particularly important as they showed that there was a permanent settlement with intense Euboic influences and it was founded there by the end of the 12th century – beginning of the 11th century b.c. The character of this premature foundation cannot be defined yet, however the new data are valuable because we learn more things about the Euboic colonial activity in the region of Halkidiki, and furthermore about the commercial relations which were developed in the North Aegean during the Dark Centuries.