However, for the purposes of this article, it’s also the document that introduced the concept of Time Immemorial.
Although often used as a general phrase for “a very long time ago”, it specifically refers to events that occurred before 3rd September 1189.
Anything before that date is time immemorial.
Explicitly why 3rd September 1189 was chosen as the barrier between that which we know and that which we don’t has itself been lost to time.
But a very good theory exists.
That date marks the coronation of King Richard (the Lionheart), the three-tims predecessor of King Edward I, and a good theory exists about why great-grand uncle was the point at which time immemorial began.
At the time, a legal policy allowed defendants to cite oral history passed down from their grandfather in disputes over land ownership. However, for the purposes of this situation, grandad could be dead, but so long as dad was still alive, and would swear that he heard it from his dad, that could stand up in court.