Harpists pluck with the pads of four fingers of each hand (never the little fingers), usually near the middle of the string. Plucking at the middle cancels every even harmonic, which is why the harp sounds so round. Touching a string at its midpoint while plucking gives a harmonic an octave higher.
Resonator String
Strings of gut, nylon and wound wire, from about C1 to G7. The C strings are dyed red and the F strings dark, so the player can find their way along a wall of strings.
Body Soundboard
The strings pull straight up from the soundboard, so the board is bent by their tension and drives the air directly. The soundbox behind it widens towards the bottom to give the long bass strings a bigger board.
Where it comes from
Harps are among the oldest stringed instruments: arched harps appear in Sumerian and Egyptian art around 3000 BC, and harps were found in the Royal Tombs of Ur. Pedals came in the 18th century; the single-action harp could raise each string by a semitone. Sébastien Érard's double action of 1810 lets each pedal raise its strings by one or two semitones, so the harp can play in every key.