In ancient Roman religion and law, the sacramentum was an oath or vow that rendered the swearer sacer, "given to the gods," in the negative sense if he violated it.[1] Sacramentum also referred to a thing that was pledged as a sacred bond, and consequently forfeit if the oath were violated.[2] Both instances imply an underlying sacratio, act of consecration.
The sacramentum differs from iusiurandum, which is more common in legal application, as for instance swearing an oath in court. A sacramentum establishes a direct relation between the person swearing (or the thing pledged in the swearing of the oath) and the gods; the iusiurandum is an oath of good faith within the human community that is in accordance with ius as witnessed by the gods.[3]
Sacramentum is the origin of the English word "sacrament", a transition in meaning pointed to by Apuleius's use of the word to refer to religious initiation.[4]