Thessalonica was founded in 315 B.C. by Cassander, a general under Alexander the Great. Cassander named the city after his wife, Alexander's half-sister. Under Roman rule, Thessalonica was the capital and largest city in Macedonia. During the 1st century A.D., the population totaled about 200,000. During the reigns of Constantine and Theodosius (A.D. 379-395) a harbor was built and Thessalonica eventually developed into a central trading center because of the importance of its seaport to the region.
Paul founded the church in Thessalonica (Acts 17:1-9). He arrived in Thessalonica after being released from prison at Philippi. The church most likely included both Jews and Gentiles, but was predominately Gentile. Paul first shared about Christ in the synagogue where he preached for three Sabbaths before he and the Jews of this city chased his companions from Thessalonica. This occurred during Paul's 2nd Missionary Journey.