From Gaulish carn, »horn, antler«: a tall, low-timbred, ∫-shaped brasswind instrument; the war-horn of the ancient Celts. These are the horns shown in numerous pieces of ancient art, such as the Gundestrup Cauldron; they were made from bronze, their bells adorned with figurative heads typically depicting boars — presumably because their sound was considered reminiscent of the cry of a boar. Reconstructed carnyces do not have a large width of register, and they do not appear to have been a recreational instrument. Rather, they were probably blown only in war, or perhaps also in other processions that were in some way grave. (To the best of my knowledge, all surviving depictions of them in a context show them as part of a march of soldiers.) Theories have been put forth that they may have been used as signal horns in battle, but the Roman writers who are as so often, we might say as always, our chief sources claim that they were merely blown to encourage the Gaulish troops and intimidate the enemy.
The carnyx is by no means the only type of Celtic horn; it is joined by such instruments as the dord, the forf, and the parp.