The ancient 'enclosed' military harbour of Thasos, was created in the middle of the east part of the ancient city, and constitutes the continuation of the land walls in the sea.

The basin is protected by the marime and coastal fortification, strengthened by circular towers in certain intervals and in the entrance of the harbour as well. The marine fortification is dated at the beginning of 5th century B.C., while the towers and an extension at the west side outside the harbour are dated at the end of 4th century. New arrangements came during the Early Christian period, when the entrance of the harbour was transferred.

Inside the harbours basin the remains of shp sheds were traced, these are dated in two phases: that of the beginninng of 5th cent. B.C., and a second phase at the end of 4th cent. B.C. The sanctuary of Goddess Soteira Ellimenias, dated between 6th cent. B.C. and 5th cent. B.C. indicates a sacred essence of the 'enclosed' military harbor, that couldn't be absent in the bastion of defence and attack of the city.

In general that monument is mentioned as an example for information about the 'enclosed' military harbors that were holding an integral part in the ancient cities and were constructed during the antiquity, from the archaic period to the late hellenistic period.