ancient history

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The history of times long past.
• noun Informal Common knowledge, especially of a recent event that has lost its original impact or importance.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun idiomatic That which happened a long time ago and not worth discussing any more.
• noun A period of history generally seen as occurring before the Middle Ages, that is, before the fall of the Roman Empire. Includes Ancient Egypt, Ancient Greece and Ancient Rome.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun knowledge of some recent fact or event that has become so commonly known that it has lost its original pertinence
• noun a history of the ancient world