Seleucia (səlōˈshə) [key], ancient city of Mesopotamia, on the Tigris below modern Baghdad. Founded (c.312 B.C.) by Seleucus I, it soon replaced Babylon as the main center for east-west commerce through the valley. The city was the eastern capital of the Seleucids until the Parthians conquered it. The Seleucids then moved their capital across the river to Ctesiphon, and Seleucia was thus superseded. In a Parthian campaign Trajan burned the city, and in A.D. 164 it was destroyed by Romans. Another Seleucia was founded by Seleucus I in Syria as the seaport for Antioch on the Orontes.
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