Magnesia, Battle of 190 or 189 B.C., a battle fought in Asia Minor near what is now Manisa, Turkey. A Roman army commanded by Lucius Scipio defeated the forces of Antiochus III, ruler of the Seleucid kingdom of Syria. This battle was the first fought by the Romans in Asia and established them as a power in the East. Antiochus agreed to abandon most of Asia Minor.