Thessaloniki was founded by Cassander in 316 or 315 BCE and named for his wife Thessalonike, a daughter of Philip II of Macedon. Its harbor and position on routes across Macedonia made it a major commercial center. Roman control began in the second century BCE, and the Via Egnatia connected the city with the Adriatic, Thrace, and Byzantium. Thessaloniki became capital of the Roman province of Macedonia, giving its civic center administrative, judicial, religious, economic, and ceremonial importance across a wide region.

The forum, often called the Ancient Agora, occupied a central area laid out in Hellenistic times and extensively rebuilt from the late second century CE. A large rectangular plaza was bordered by two-story colonnades and public buildings. An odeon or small theater stood along one side, while baths, administrative rooms, shops, archives, and ceremonial spaces occupied neighboring terraces. A cryptoporticus below the upper level supported the complex and provided covered circulation. Marble paving, sculpture, fountains, and inscriptions expressed metropolitan wealth and Roman civic identity.

The complex changed over several centuries rather than following one fixed plan. The odeon was enlarged and may have accommodated staged spectacles in addition to music and civic gatherings. Sculptural groups and the famous colonnade known as Las Incantadas probably belonged to the broader public center; those figures were removed to France in the nineteenth century and are now in the Louvre. By late antiquity, Christianity, imperial residence, new streets, and shifting commercial activity transformed Thessaloniki, yet parts of the forum remained in use into the sixth century.

The ruins were unexpectedly exposed during excavation for a planned courthouse in the 1960s. Public debate and archaeological intervention stopped construction on the site, though the surrounding square retained its popular association with the courthouse project. Excavation revealed the forum’s terraces and forced modern planners to accommodate a major ancient precinct within the dense city. Conservation stabilized walls, paving, columns, and the odeon, while an underground museum was created within the restored cryptoporticus to display finds and explain successive phases.

The museum’s sculpture, pottery, coins, inscriptions, and everyday objects extend the story from the Hellenistic city through the Roman, early Christian, Ottoman, and modern periods. The open archaeological area above remains embedded among apartments, streets, shops, and public squares. This setting makes the forum a record of both ancient government and modern urban choice. Thessaloniki preserved the complex not as an isolated ruin outside town, but as evidence that the contemporary city has repeatedly rebuilt over the same strategic center for more than two thousand years.