The instrument's modern form and proportions were strongly influenced by the maker Pasquale Vinaccia of Naples (1806–82). The mandolin has four pairs of steel strings tuned, by a machine head (as on a guitar), to violin pitch (g–d′–a′–e″); the pegs are at the back of the pegbox. The pear-shaped body is deeply vaulted; the fingerboard, with 17 frets, is slightly raised. The strings are hitched to the instrument's end. At its widest part, where the bridge is set, the belly angles downward, increasing the pressure of the strings on the bridge to give a brilliant tone of great carrying power. (The mandolin played in American bluegrass string bands is a shallow, flat-backed version of the instrument.) Quick movement of the plectrum across each unison pair of strings produces a characteristic tremolo. A shell plate around the oval sound hole protects the belly from damage by the plectrum. Mandolin playing and making flourished in Europe and in the Americas in the late 19th and early 20th centuries. In the 20th century the mandolin was built in a family of sizes from soprano to contrabass. Compositions for the mandolin include a concerto by Antonio Vivaldi, the serenade in Mozart's opera Don Giovanni (1787), and parts of Igor Stravinsky's ballet Agon (1957).