For some reason I remember learning years ago - I don't know when - that it first originated in ancient Egypt. Is this true? I've been unable to find any evidence of the Egyptians being the first people to practice it, or even if they followed it. If they didn't create it, then who did?
It dates at least ot the Romans, but I don't know if our version of it traces directly from them or was reinvented in modern times.
A fundamental principle of Roman law is that the burden of proof lies on him who asserts something (i.e., usually the accuser). This makes it into the Digest of Justinian (22.3) as Ei incumbit probatio qui dicit, non qui negat, "Evidence is impendent upon him who claims, not him who denies." The Digest is a late work but is a sort of summary and codification of principles that had long been in existence (as if someone should codify and write down all of English common law), and this particilar principle is very old.
According to Ammianus Marcellinus (18.1), the emperor Julian put this in a very memorable form. When someone attempted to prove that an official had been guilty of embezzlement, he asked Julian, "Who will ever be found guilty, if it be sufficient to deny the charge?" To this, Julian replied, "Who will ever be found innocent, if it be sufficient to accuse?"
Follow up question on the standard of proof. When was "beyond reasonable doubt" adopted?