The ius fetiale of Antiquity was the set of rules and regulations under which treaties (foedera, sg. foedus) were to be handled. It was among the iura sacra, and its overseers and interpreters were the fetiales. It is frequently mentioned alongside its important counterpart, used in connection to declarations of war and the conduct thereof, the ius gentium.
History of the ius fetiale
Plutarch, Livy, Cicero, and Dionysius of Halicarnassus, among others, all give interpretations of the institution of the fetiales at Rome, though some disagree with others. However, none of them give much, if any, insight into the development of the ius fetiale, though it might be asserted that the beginnings of the ius fetiale at Rome would have come to the city at the same time, and by the same means. On that, then, it might be taken from Livy, who ascribes Ancus Marcius with the institution of the fetiales, that the ius fetiale came to Rome by the Aequicoli 1.32.5; however, that remains uncertain.
The earliest use of the ius fetiale is found in the work of Livy as well; in his history, he records the treaty made between the Romans and the Albans prior to the fight of the Horatii and the Curiatii 1.24.3.
- Watson, Alan. International Law in Archaic Rome: War and Religion. ISBN 0801845068