An individual priest of the collegium was a fetialis. He held the office for life.
Livy is the main source of information on the fetials, who are believed to have been formed by one of the Roman kings, specifically, Numa, Tullius Hostilius, or Ancus Martius.
The practice of having a fetial priest officiate at the commencement and end of war is thought to have been adopted from other Latin states. While the office of fetials may have lapsed at the end of the Republic, Augustus revived it.
The fetials would choose one of their number as pater patratus who would declare war by hurling a spear, tipped with iron or charred and smeared with blood, into enemy territory unless the enemy was too distant. If too far, the spear would be hurled into an area of the temple of the goddess Bellona.
A fetial also made peace treaties official by cursing Rome should it be the first to break the treaty.
Sources:
Adkins and Adkins: Dictionary of Roman Religion.
Lacus Curtius - Smith Dictionary - Fetialis.
