The World in a Tuba
The image was taken in Madrid.
An orchestra usually has a single tuba, though an additional tuba may be asked for. It serves as the bass of the orchestral brass section and it can reinforce the bass voices of the strings and woodwinds. It provides the bass of brass quintets and choirs (though many small brass ensembles will use the euphonium or bass trombone as the lowest voice). It is the principal bass instrument in concert bands, brass bands and military bands, and those ensembles generally have two to four tubas. It is also a solo instrument.