The cornu was a brass instrument used in ancient Rome. Its name literally means "horn" in Latin. It was a massive instrument, with a tube that could stretch up to 11 feet long. This tube was curved into a distinctive 'G' shape, making it one of the more recognizable instruments of the era.

Because of its size and weight, the cornu was unwieldy. To make it playable, especially while marching, it featured a crossbar. This brace ran across the open part of the 'G' and allowed the player, known as a cornicen, to rest the instrument comfortably on their shoulder. This design distributed the weight and kept the instrument stable, freeing the player's hands to manage the mouthpiece and support the instrument.

The cornu's primary role was as a signaling device, especially within the Roman army. Its loud, deep tone could carry over the noise of a bustling camp or a chaotic battlefield. The cornicen was a standard-bearer, positioned near the commander to relay orders to the troops. Different calls would signal actions like advancing, retreating, changing formation, or sounding a charge.

Beyond the battlefield, the cornu was a fixture at public events. Its powerful sound added gravity to state ceremonies and religious processions. It was also part of the orchestra of the arena, played during gladiatorial games to announce the start of combat and heighten the drama for the crowd.

This dual use in both military and civic life shows how integral the instrument was to the soundscape of ancient Rome. It was the sound of order, power, and spectacle.

The cornu was a simple but effective tool, shaping Roman life both in times of war and peace.