How are ancient documents authenticated?

Think of the ancient documents rule like an old family recipe passed down for generations - it's trusted because it's been around for so long. It's also unlikely that 20 years ago, someone lied in the record for the purpose of manipulating a court case 2 decades later. Thus, in Federal court, any paper that's 20 years or older, in a condition that creates no suspicion about its authenticity, and found in a place where such a document would likely be kept, gets this kind of trust. It's assumed to be real or authentic. This rule is handy because, after so many years, proving a document is genuine can be really tough. It's like giving the benefit of the doubt to old documents in legal matters, making things simpler when dealing with really old papers.