The very extensive archaeological site of Demetrias includes the prehistoric settlement at Pefkakia and the Hellenistic, Roman and Late Roman city with its public buildings, palace, private houses, sanctuaries and cemeteries. Much of the city's impressive fortifications still remain. They consist of ramparts and bastions, which culminate in the northwest in a fortified acropolis. In the western part of the city, near the Athens-Volos highway, are the first Hellenistic buildings: the Hero?n, which was probably a temple or a mausoleum, the theatre, which remained in use until the fourth century AD, and a house with internal court, private shrine and an area for repairing clay vases with lead clamps and for making lead loom-weights. In the same area, a row of pillars of the huge aqueduct of the fourth century AD crosses the highway. On a small rise inside the city is the Hellenistic two-storied palatial complex, which functioned until the second century BC. Part of it was used as a cemetery in Roman times. South of the palace is the forum, the financial and administrative centre of the city, with the temple of Artemis Iolkia. The relatively flat area between the palace hill and the southeast city wall is now covered with almond and olive trees. In the northeast sector of the city, next to a pine grove, excavations revealed a Hellenistic building with peristyle, probably a Metro?n, where Cybele, mother of the gods, and other deities were worshipped during the period of great prosperity for Demetrias. The small bay to the north of the city was originally the royal port. This area became the centre of the Roman and Late Roman city, of which several buildings have been uncovered. Some of the Roman structures have mosaic floors, baths and staircases. One of them, on the seafront, probably a public building, had large rooms containing amphorae and coins. The Basilica of Damokratia, the most important Early Christian monument of Demetrias, is also located in this sector. A traditional shipyard and the museum of folk artist N. Christopoulos, a shipbuilder who lived at Pefkakia and drew inspiration from sea life, occupy today the Pefkakia promontory.

Several houses of the Hellenistic and Roman periods have been excavated in the city. The Hellenistic houses had central, often peristyle, courtyards, shrines and storerooms, and were separated by streets, 3.5 - 4.0 metres wide, with drains. In Roman times the city had several luxurious private mansions. The north, south and east cemeteries of the city lie outside the city walls, while the west acropolis lies within the enclosure, to the north of the theatre.