On the flat surface of Cape Posidi, 4 km west of the city, the excavation brought to light the sanctuary of Mendes, which was dedicated to Neptune. As the geological survey found, the sanctuary occupies the entire area of a sandy peninsula, about 150 meters wide and 60 in width, so that its buildings are projected into the sea, like the corresponding temples in Sounio and Naxos. The geomorphology of the cape has changed significantly since antiquity to date, due to sand deposits and shifts from storms and large seismic fractures. The dense arrangement of the four buildings currently under investigation suggests the lack of available space, but no building seems to have substantially eliminated the use of the oldest, while the fragmentation of several foundations was quite fragmented.
The temple, which is the oldest sanctuary of Poseidon, has been in operation for more than 1000 years, and there are references to it still by Thucydides and 14th-century Athonite documents. It was probably built by the Eretrians, who colonized Mendes and had their protector Neptune.
The excavations brought to light four large buildings: the main temple, two buildings on either side of the temple, and an arched building in the eastern part of it. The latter, which is the oldest, dates from the Protogeometric period (11th-10th centuries BC). Its flooring is clay and the walls are made of large pebbles.
The rest of the buildings date back to the 7th-6th century BC. century, while the main church from the 5th century BC. c. All buildings were devotional and there are altars everywhere for sacrifices and places for sacred ceremonies. In 1864 it was built on the edge of the cape and a beacon that survives until today