The Pergamon Altar was a monumental construction built during the reign of the Ancient Greek King Eumenes II of the Pergamon Empire in the first half of the 2nd century BC on one of the terraces of the acropolis of Pergamon in Asia Minor. It was described as one of the Seven Wonders of the Ancient World by three known classical lists. 4 metres deep; the front stairway alone was almost 20 metres wide.