The harp is a stringed musical instrument. It has a large triangular wooden frame. The modern harp has 46 or 47 strings of graduated lengths stretched between the instrument's two sides, called the sound box and the neck. The third side, known as the pillar, contains rods that are operated by seven pedals at the base of the harp. The rods activate a mechanism in the neck that controls changes in pitch. Musical tones are produced by plucking the strings with the fingers. Harps of this kind are known as double pedal or double-action harps. They are generally tuned to the key of C flat major. Although the strings would follow the diatonic scale if played alone, use of the pedals makes it possible to play a chromatic scale, or all the notes in a given octave.
One of the oldest instruments in the world, the harp appears in Egyptian and Sumerian art as early as 3000 B.C. A form of the harp was also played by the ancient Greeks and Romans. During the Middle Ages a harp similar in form to the modern type was developed in northern Europe. By the 10th century the instrument had become very popular throughout the British Isles, notably in Ireland. The first pedal harp was invented by Celestin Hochbrucker in 1720. His harp was superseded by the double-action harp, which was invented by Sebastien Erard in about 1810. After the introduction of Erard's harp the instrument began to be widely used in the orchestra. It figured prominently in the works of such composers as Berlioz, Liszt, Tchaikovsky, Debussy, and Ravel.
The harp is distinguished by its silvery tone. It is especially suited to the playing of the glissando, a rapid scale performed by sliding the hand quickly over the strings. Composers have frequently used the instrument to suggest celestial music. The harp is the national emblem of Ireland.