Year 189 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Nobilior and Vulso (or, less frequently, year 565 Ab urbe condita). The denomination 189 BC for this year has been used since the early medieval period, when the Anno Dominicalendar era became the prevalent method in Europe for naming years.
The defeat of Antiochus III by the Romans in the Battle of Magnesia robs the Aetolian League of its principal foreign ally and makes it impossible for them to stand alone in continued opposition to Rome. The League is forced to sign a peace treaty with Rome that makes it a subject ally of the Republic. Although the League continues to exist in name, the power of the League is broken by the treaty and it never again constitutes a significant political or military force.
The city of Philadelphia (now Alaşehir, Turkey) is founded by King Eumenes II of Pergamon. Eumenes names the city after his brother, Attalus, whose loyalty earns him the nickname, "Philadelphus", literally meaning "one who loves his brother".