I'm not sure if Thessalonike was formed before Antioch. In any case, Thessalonike never played an important role in history in this time, as has Antioch (Being the capital of the Seleucids). Thessalonike was just an autonomous city-state and little more I know through until Roman days.
EDIT: Seeing Thalakos post in the Open Beta Thread, actually Antioch was founded a year before Thessalonike.
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