The ancient city of Pergamon (also Pergamum or Pergamos) stood at the top of a steep hill that overlooks the modern Turkish city of Bergama. Because of this highly defensible position, the Macedonian general Lysimachus chose it as a stronghold for his treasures in the 4th century BCE.
Over succeeding centuries, Pergamon forged an alliance with Rome and became both a powerful city and an important center of art, literature and learning.
In 133 BCE, the ruler, Attalus III Philometor, died without heirs and bequeathed the city to Rome. As part of the Roman Empire, Pergamon continued to flourish and became the capital of the Roman province of Asia.
While the ruins of Pergamon pale by comparison to those at Ephesus, if you are in the area of the modern city of Izmir (perhaps to see Ephesus), Pergamon is nearby and well worth the trip.
For more ruins, check out the separate Ephesus page.