fetial

A member of the Roman college of priests who acted as representatives in disputes with foreign nations.

Nicomachus, as explained in the next line, was already known to the Elean priests or fetials, or whatever we are to call them, as a guest-friend.

It was customary for the fetial to carry to the bounds of the other nation a cornetwood spear, iron-pointed or hardened in the fire, and in the presence of not less than three grown men to say, "Whereas the tribes of the Ancient Latins and men of the Ancient Latins have been guilty of acts and offences against the Roman People of the Quirites; […] I therefore and the Roman People declare and make war on the tribes of the Ancient Latins and the men of the Ancient Latins." Having said this, he would hurl his spear into their territory.

Of or relating to a fetial (member of the Roman college of priests who acted as representatives in disputes with foreign nations); (by extension) ambassadorial, heraldic.

[P]erhaps the shadowy fetials were never actually an independent priesthood but were senatorial priests assigned diplomatic functions. If fetials were originally senators, this would explain the parallel fetial and senatorial function in "international relations" and account for the continuity between fetials and later senatorial legates.

Concerned with declarations of war and treaties of peace.

The institution of a college of heralds and the fecial law, were proofs of a people considerably advanced in the cultivation of the law of nations as a science; and yet with what little attention they were accustomed to listen to the voice of justice and humanity, […]

With the Fetial Law we are only imperfectly acquainted, but it seems to have been simply a law peculiar to the Romans, and regulating their conduct towards foreigners, and not properly an international law common to other nations, and determining on general principles their respective rights and duties.