Developed in antiquity—in places unknown—to guarantee the truthfulness of the speaker's words, the taking of oaths is now a universal custom. The need for oaths arose as human society became more complex. Business depended on the viability of promises, and jurisprudence depended on testimony that was true. In time, every political, commercial and jurisprudential body required an effective means to assure its decisions and judgments were based on genuine, truthful evidence. 

Despite the importance of Truth, it is elusive. In human efforts to prove truthfulness, we have experimented with trial by fire, by combat, by dunking, by hot irons and by boiling water. Although awkward, these means all revealed the criminal or the liar by leaving truthful or innocent subjects unmarked after a harrowing ordeal. There was even trial by host, reserved for members of the clergy. In this clever proceeding, a cleric who had been accused of a crime would declare his (they were usually men) innocence in a loud and public way before an altar of God. If the cleric had spoken falsely, God would strangle him to death on the spot. This gruesome test effected such honest testimony that no one has died in this grisly ritual since 1163.