Wikipedia
The saxotromba is a valved brasswind instrument invented by the Belgian instrument-maker Adolphe Sax around 1844. It was designed for the mounted bands of the French military, probably as a substitute for the French horn. The saxotrombas comprised a family of half-tube instruments of different pitches. By about 1867 the saxotromba was no longer being used by the French military, but specimens of various sizes continued to be manufactured until the early decades of the twentieth century, during which time the instrument made sporadic appearances in the opera house, both in the pit and on stage. The instrument is often confused with the closely related saxhorn.
The technical specifications of the saxotromba and the original constitution of its family are not known with any certainty. Initially, the instrument had the same vertical design as its close relation the saxhorn, with the bell pointing upwards, though later models of both families were designed with bells that faced forwards (pavillon tournant). The mouthpiece was cup-shaped, and the bore was conical, being probably intermediate between the cylindrical bore of the natural trumpet and the conical bore of the natural horn; the taper was slower than that of the saxhorns and cornets.
The name of the instrument combines Sax's surname with the Italian word for "trumpet" (tromba). In Germany the instrument is known by the name Saxtromba; in France the term saxotromba is generally applied to another close relative, the Wagner tuba.