Sardica

The history of Sofia, Bulgaria's capital and largest city, spans thousands of years from Antiquity to modern times, during which the city has been a commercial, industrial, cultural and economic centre in its region and the Balkans.

Sofia was originally a Thracian settlement called Serdica or Sardica, possibly named after the Thracian tribe Serdi that had populated it. For a short period during the 4th century B.C., the city was possessed by Philip of Macedon and his son Alexander the Great.

Around 29 B.C., Sofia was conquered by the Romans and renamed Ulpia Serdica. It became a municipium, or centre of an administrative region, during the reign of Emperor Trajan (98-117). The city expanded, as turrets, protective walls, public baths, administrative and cult buildings, a civic basilica and a large amphitheatre called Bouleutherion, were built. When Emperor Diocletian divided the province of Dacia into Dacia Ripensis (on the banks of the Danube) and Dacia Mediterranea, Serdica became the capital of Dacia Mediterranea. The Edict of Toleration by Galerius was issued in 311 in Serdica by the Roman emperor Galerius, officially ending the Diocletianic persecution of Christianity. The Edict implicitly granted Christianity the status of "religio licita", a worship recognized and accepted by the Roman Empire. It was the first edict legalizing Christianity, preceding the Edict of Milan by two years. The city subsequently expanded for a century and a half, which caused Constantine the Great to call it "my Rome". In 343 A.D., the Council of Sardica was held in the city, in a church located where the current 6th century Church of Saint Sofia was later built.

...
Wikipedia