The baritone horn is a popular low brass instrument used in many marching bands, concert bands and orchestras. In shape, it resembles a tuba. The musical range of the baritone is from approximately E on the line below the bass clef staff to the C above the treble clef staff.
The baritone horn's earliest known ancestor is believed to be a wooden instrument called the serpent. Like the modern baritone, the serpent used a cup-shaped mouthpiece and the musician was required to buzz his or her lips into the mouthpiece in order to produce a low, mellow tone.
Unlike the modern baritone, the serpent had no keys and players had very little ability to modulate which notes it played.
In 1817, Jean Hilaire Asté took a new idea---the keyed bugle, which added keys like a clarinet to brass instruments---to create the next ancestor of the modern baritone. He called his instrument the ophicleide.
The ophicleide was made of brass instead of wood and its shape was less round and sinuous than the Serpent had been and more like the upright folded shape of as bassoon.
Ophicleides were frequently used in orchestras and bands through the 19th century and their sound became a feature of orchestra music of the time. Felix Mendelssohn used it in his score for "A Midsummer Night's Dream" to imitate the sound of an ass braying. Berlioz scored his Symphonie Fantastique to feature the sound of at least two ophicleides.
In 1818, Heinrich Stölzel was issued the first patent for a rotary-valve system on a musical instrument. Valves allowed the musician to change the length of the horn, and thus the sound, very slightly, which then allowed brass instruments to play each note in a scale.
Valved instruments in each range followed quickly. The valved trumpet was the top range---the soprano; the tuba the lowest range---the bass, and a range of mid-sized brass instruments were created for the middle ranges---alto, tenor and baritone.
The instrument that most resembles today's baritone was know as the tenor horn. This was a mid-sized brass instrument, keyed in B-flat like the tuba, which could be played throughout the mid-range of most instrumental music. Its wide, flared bell gave it a mellow sound with a bright finish in its higher ranges.
The arrangement and tubing of the brass tenor horn, or baritone, as it was coming to be known, made it a challenge to play and move at the same time. However, music was an integral part of the military experience, rendering it necessary to create a horn that had a similar sound to the baritone, as well as having its range.
Early marching tenor/baritone horns had a variety of designs. One of the more popular was the "over-the-shoulder" horn design, in which the bell pointed backward over the musician's shoulder, allowing the soldiers marching behind to hear the music clearly and stay in step.
Eventually, the design of the "marching baritone" settled into a style resembling a large, flared-bell trumpet. Also known as the bass cornet, this design survives today and is used in most marching bands that wish to have a baritone sound.
Baritones today are featured in many marching bands, drum and bugle corps and orchestras. However, the baritone often is confused with another brass instrument with a similar sound and range: the euphonium. The two horns do share features and characteristics, including the upright playing stance resembling a tuba and the flared upward-pointing bell.
However, the euphonium generally has four valves rather than three and a considerably larger amount of tubing in the makeup of the horn. Euphoniums also feature a mellower, less brassy sound and a slightly broader range (depending on the player) and thus are actually more common in bands and orchestras today than genuine baritone horns.