An ancient document, in the law of evidence, refers to both a means of authentication for a piece of documentary evidence, and an exception to the hearsay rule.
Authentication
With respect to authentication, an "ancient document" is one that may be deemed authentic without a witness to attest to the circumstances of its creation because its age suggests that it is unlikely to have been falsified in anticipation of the litigation in which it is introduced.
Under the American Federal Rules of Evidence ("FRE"), a document is deemed authentic if it is: