“Diateichisma” was built by the Athenians at the end of the 4th century B.C. in order to confront the approaching danger from Macedonians. The new wall, which established a boundary on the crests of the Hill of the Mouses (Philopappos), the Pnyx, and the Hill of the Nymphs and at the north and south connected with the older Themistoklean Wall, reduced the extent of the fortified area of the city at the west, leaving unprotected large part of the Demes of Melite and Koile. This middle wall, 900 metres long, which was built according to the “emplekto” system (compartment wall), had two gates at its junctures with the Hills and was fortified with rectangular and circular towers. In the middle of the 3rd century B.C. “Diateihisma” saw extensive repair in white poros-stone, the “emlpekto” technique was abandoned, and its course in the area of the Pnyx was modified. In Justinian times, at 6th century A.D. , the Diateihisma reinforced and kept in new repair with more towers added. Post-byzantine manuscripts recall Justinianic activity here when they refer to the “Royal Wall”.
The south gate of the Diateihisma, between the Hill of the Mouses and Pnyx, at the axis of the most important commercial and traffic artery of Athens the “Road through Koile”, is indentified, thanks to an ancient inscription, as the “Dipylon over the Gates”. East of the gate is a small roadside shrine epigraphically recorded as dedicated to the homeric hero Aias or to Herakles, Athena and Demos, as protectors of the Gates. From byzantine era the militant Saint Demetrios Loumbardiares has been workshipped at the spot. The north gate between Pnyx and the Hill of the Nymphs has been indentified as the “Meletides Gates” mentioned in the literary sources.
From the 4thcentury B.C. up to medieval times, “Diateihisma” kept in repair, served as a first line of defence for the city of Athens from the west. Today “Diateichisma” is preserved or can be traced along its whole length and gives important topographical evidence for the defense of Athens. Of the “Dipylon over the Gates” near the church of Saint Demetrios Loumbardiares, now partly covered with décor designed by the architect Pikiones, remains of only the South side of the tower are preserved.