Throughout the history of stringed instruments, the strings have been made out of the animal gut. Of course, there are piano concertos and pieces of music that require a piano, but the piano will be an addition to the standard set-up of an orchestra. Also, the piano is not part of a standard orchestra. This is because the strings are hit with hammers like a percussion instrument - such as the timpani or xylophone. The piano, although it has strings - 230 of them actually - is classified as a percussion instrument. It is not considered part of the string family, however, but a unique instrument in its own right. It usually has 47 strings which are plucked with the fingers, and seven pedals, each with three positions. We must not forget about the harp which is part of a modern symphony orchestra. It sounded one octave lower than the double bass.
In the 19th Century, someone designed and built an Octobass which was so huge it made it incredibly difficult to transport, let alone play.
It is different from the other three instruments of the string family in that it is tuned to perfect fourths, unlike the others which are tuned to perfect fifths.
The popularity of Baroque music brings stringed instruments into more familiar territory as they start to be used in orchestras as we know them today: a family of four - the highest notes from the violin, followed by the viola, then the cello and finally, the lowest sounding orchestral stringed instrument: the bass, also known as the contrabass or double bass, which was only gradually accepted into the orchestra after years of arguments about how it should be tuned.