In 379 , when the Roman Prefecture of Illyricum was divided between the East and West Roman Empires , Thessaloniki became the capital of the new Prefecture of Illyricum . The following year , the Edict of Thessalonica made Christianity the state religion of the Roman Empire . In 390 , Gothic troops under the Roman Emperor Theodosius I , led a massacre against the inhabitants of Thessalonica , who had risen in revolt against the Gothic soldiers . By the time of the Fall of Rome in 476 , Thessaloniki was the second-largest city of the Eastern Roman Empire
massacre against the inhabitants of Thessalonica
Massacre of Thessalonica
Thessaloniki