The harp is a stringed musical instrument consisting of a rigid, triangular frame within which are stretched a set of parallel strings. The strings run between the top, or neck, of the harp, and its resonator. Ancient and primitive harps lacked the third rigid member of contemporary frame harps, the pillar, which extends from the neck down to the lower end of the resonator. The strong structure provided by the pillar allows for an increased string tension that produces notes of a higher pitch than was possible with early harps. The instrument is played by tilting it back so that it rests against the player's shoulder, and plucking the strings from either side with the fingers of both hands.
The modern orchestral harp stands approximately 170 cm (5.5 ft) high and has the largest range in the orchestra: more than 5 ½ octaves (the lowest note is C-flat below the bass staff). At the base of the harp are seven pedals, one for each degree of the diatomic scale. These pedals mechanically connected through the pillar to two rows of rotating pronged discs placed under the strings on the neck, enable the player to raise the pitch of all of the strings for each degree of the scale either a semitone (pedal at half hitch activating discs in the first row) or a whole tone (pedal fully depressed activating discs in the second row); the instrument is thus totally chromatic (a sequence of notes proceeding by semitones). The harp is strung in gut or nylon in the upper and middle registers. The bass strings are of over spun wire.
The chromatic flexibility offered by the pedal harp, along with a growing thirst for orchestral color, made the harp increasingly appealing to 19th-century composers. The instrument became a regular member of the orchestra of Berlioz, Wagner, and Tchaikovksy.