To ancient peoples, oaths were very important things and were taken with the utmost seriousness. In keeping with the theme of this blog, however, I’ll be centering on the Roman practices of oath-taking.
The Oxford Dictionary of Classical Myth & Religion has this to say:
An oath was a statement or promise strengthened by the invocation of a god as a witness and often with the addition of a curse in case of perjury. A defendant in a lawsuit, for example, might swear by a god that his testimony was truthful and might specify the punishment for perjury. If the oath was false, the god, by effecting the provisions of the curse, would punish the individual, not for lying in court but for committing perjury. Throughout antiquity oaths were required of signatories to treaties, of parties to legal disputes, commercial and private contracts, conspiracies, and marriages, of governmental officials, judges, and jurors, and, particularly by the Romans, of soldiers (sacramentum), and, under the empire, of citizens to affirm their allegiance to the emperor.
Typically, the Romans called upon “Iuppiter, Dius Fidius and all the gods”. Dius Fidius is a god associated with Iuppiter, but is clearly a separate deity. His full name is Semo Sancus Dius Fidius, or Sancus or Dius Fidius for short. His name comes either from the Latin fides, or trust (who is also a goddess), or from filius, or son – as Dius Fidius is mythically the son of Iuppiter. Apparently, his temple had no roof so that people could swear oaths directly under the sky and thus the view of the god.
People often used oaths in casual speech as well, much like our exasperated “Oh god!” today: women generally swore by Castor, men by Pollux and Hercules. The Latin phrase “Mehercule!” appears as a sort of oath, meaning “By Hercules!”
Treaties, one of the most (if not the most) important oaths that could be sworn were sworn by Iuppiter Lapis. This aspect of Iuppiter, the Stone, was located in the temple of Iuppiter Optimus Maximus on the Capitoline Hill. Like its name may suggest, this was a stone representing Iuppiter in his aspect of one who presides over oath-taking.
The punishment for oath-breaking was severe: this was often death for the perjurer, and sometimes his family as well.
As a side note to oaths and a fun fact: contrary to popular belief, the Romans did not swear oaths in court by grabbing their testicles. The word for witness, testis, lends itself to “testimony” and not “testicles”.