Titus Livius (Livy), The History of Rome, Book 1
Rev. Canon Roberts, Ed.

24. There¹ happened to be in each of the armies a triplet of brothers, fairly matched in years and strength. It is generally agreed that they were called Horatii and Curiatii. Few incidents in antiquity have been more widely celebrated, yet in spite of its celebrity there is a discrepancy in the accounts as to which nation each belonged. There are authorities on both sides, but I find that the majority give the name of Horatii to the Romans, and my sympathies lead me to follow them.

[2] The kings suggested to them that they should each fight on behalf of their country, and where victory rested, there should be the sovereignty. They raised no objection; so the time and place were fixed. [3] But before they engaged a treaty was concluded between the Romans and the Albans, providing that the nation whose representatives proved victorious should receive the peaceable submission of the other.

This is the earliest treaty recorded, and as all treaties, however different the conditions they contain, are concluded with the same forms, I will describe the forms with which this one was concluded as handed down by tradition. [4] The Fetial put the formal question to Tullus: ‘Do you, King, order me to make a treaty with the Pater Patratus of the Alban nation?’ On the king replying in the affirmative, the Fetial said: ‘I demand of thee, King, some tufts of grass.’ The king replied: ‘Take those that are pure.’ [5] The Fetial brought pure grass from the Citadel. Then he asked the king: ‘Do you constitute me the plenipotentiary of the People of Rome, the Quirites, sanctioning also my vessels and comrades?’ To which the king replied: ‘So far as may be without hurt to myself and the People of Rome, the Quirites, I do.’ [6] The Fetial was M. Valerius. He made Spurius Furius the Pater Patratus by touching his head and hair with the grass. Then the Pater Patratus, who is constituted for the purpose of giving the treaty the religious sanction of an oath, did so by a long formula in verse, which it is not worth while to quote. [7] After reciting the conditions he said: ‘Hear, 0 Jupiter, hear! thou Pater Patratus of the people of Alba! Hear ye, too, people of Alba! As these conditions have been publicly rehearsed from first to last, from these tablets, in perfect good faith, and inasmuch as they have here and now been most clearly understood, so these conditions the People of Rome will not be the first to go back from. [8] If they shall, in their national council, with false and malicious intent be the first to go back, then do thou, Jupiter, on that day, so smite the People of Rome, even as I here and now shall smite this swine, and smite them so much the more heavily, as thou art greater in power and might.’ [9] With these words he struck the swine with a flint. In similar wise the Albans recited their oath and formularies through their own dictator and their priests.