The Sanctuary of Messou is located in the homonymous valley, 35 km from Mytilini, 5 km from ancient Pyrrha and 7.5 km from ancient Arisvi. Its name is due to its location in the middle of the island. The first reference to the sanctuary was made by the French traveler M. Boutan, while the German R. Koldewey carried out the first excavations in December 1885 and January 1886. Subsequent excavations were carried out in the period 1965-67 by the then Superintendent II Petrakos , while there was also a collection of its architectural members scattered in the area of the sanctuary and in the wider area of the bay of Kalloni.
The Sanctuary of Messou, a center of worship and seat of the “Common of the Lesbians”, is located within the boundaries of the territory of ancient Pyrrha. In the archaic times, the first religious building was constructed, with a rectangular plan and altars, the remains of which are preserved within the foundation of the late classical temple (330-300 BC).
The temple is pseudo dipteran Ionic with 8X14 columns. Its dimensions are 41.55 X 23.78 m. It is preserved particularly damaged at the level of the foundation and in part of the lower structure of the three-tier platform. From the first excavation research at the end of the 19th century until today, thousands of fragments from the brutally damaged monument have been studied, restoring its original form. The wing frieze consists of a three-banded epistile, an unadorned frieze, which are crowned with Ionic waves.
The Sanctuary according to the prevailing opinion was dedicated to the Lesbian Trinity (Zeus, Hera and Dionysus). After its destruction in the late Roman era, the site acquired a laboratory use, which is documented by the discovery of 7 furnaces. In the early Christian era, on the floor of the ancient church, an early Christian cemetery royal traces were established, the traces of which can be seen mainly in the east. The basilica was succeeded by the mid-Byzantine one-room church dedicated to the worship of Taxiarch Michael, whose worship continues to this day.