During the French Wars of Religion, two factions developed at court. One loyal to Henry III, King of France (pictured on the left) and the other supporters of Henry, Duke of Guise (shown on the right). In April 1578, men from both groups pledged to fight a duel, possibly to resolve a dispute over the affections of a young lady.
So, on 27th April, Henry III’s favourites, known as mignons (‘dainties’) – Jacques de Caylus, Jean d’Arcès and Louis de Maugiron – engaged in battle with the Guise faction – Charles de Balzac, Georges de Schomberg, and Ribérac. Only d’Arcès and Balzac survived the duel; Maugiron and Schomberg died on the field; Caylus took thirty-three hours to die from his wounds.
This duel may have been a re-enactment of the battle between two sets of triplets called Horatii and the Curiatii. These two sets of brothers fought in order to decide the result of a war between ancient Rome and the central Italian city of Alba Longa. Although, this may have been a later attempt to romanticise the pointless loss of life.
To read a (somewhat biased) account of the duel and the Wars Of Religion in France you can read the Memoirs of Henry the Great at Google Books. This Henry was the King of Navarre who became King Henry IV of France after converting from Protestantism to Catholicism, saying that “Paris is worth a mass.”