On July 13 of every year, there is a something curious going on at around 10 o'clock in the morning on a remote mountain of the Pyrenees: people of the Baretous Valley in Bearn, France gave the people from the Roncal Valley in Navarre, Spain, 3 cows as a peace tribute.
According to legend, the whole thing started in 1375, when a Roncalese farmer met a Baretous Valley farmer and a quarrel ensued over grazing rights. The war of words turned deadly and before you know it, the two villages were at war.
After a particularly bloody battle, the feud was settled in one of the world's oldest peace treaties: The Tribute of the Three Cows, where the people of Baretous gave the Roncalese a yearly of 3 cows.
Then the Roncalese mayor asks in a loud voice: “Are you coming, as in past years, to pay the tribute?” The mayors from Baretous respond, also in Spanish, “We are, señor.” The Roncalese mayor asks the same question a second and third time, each time receiving the same response. Then the president of the mayors calls out the same formula repeated since bygone times: “Pax avant!” [So, let there be peace.] The mayors of Baretous repeat the words.
This has gone on every year since 1375 (with only two exceptions, one during the War of the Convention between France and Spain, and one during Nazi occupation of southern France), and every year the ceremony gets more and more popular.
Here's the story of the Tribute of the Three Cows: Link