The bugle is a simple signaling brass instrument with a wide conical bore that normally has no valves or other pitch-altering devices, and is thus limited to its natural harmonic notes. The modern bugle is made from metal tubing and that technology has roots that date back to the Roman Empire. Historically, horns were curved trumpets, conical, often made from ox or other animal horns, from shells, from hollowed ivory such as the olifant. One of the variations was to create "sickle-shaped" horns or "hunting horns" in the 15th century, which by the 18th century, were bent further into a loop, possibly first by William Shaw of London. Bugles were used militarily as a signaling instrument from this point. Today, it is still used in military ceremonies and is also popular in some music genres, such as drum and bugle corps, military marching bands, and traditional jazz.