Short answers, pulled from the story.
The mandolin became popular in 1787 when Luigi Bassi played it in Mozart's opera Don Giovanni in Vienna. It evolved from European lutes and gained global fame through virtuosi like Carlo Curti and Giuseppe Pettine in the early 20th century.
A standard mandolin features four courses of doubled strings tuned in unison, creating a total of eight strings. The tuning typically follows the pattern G3, D4, A4, E4, which is the same as the violin.
The Neapolitan bowlback has a deep bottom constructed from strips of wood glued into a bowl shape and a scale length of about 33 centimeters. The American archtop emerged at the end of the 19th century in the United States and features an arched top and shallower back carved from solid wood.
The transition from gut strings to metal strings occurred during the 18th and 19th centuries, fundamentally altering the instrument's construction. Bartolomeo Bortolazzi noted in his 1805 mandolin method that wire-strung mandolins were uncomfortable to play compared to the softer gut strings of earlier centuries.
Antonio Vivaldi created concertos for mandolinos and orchestra, while Ludwig van Beethoven composed four small pieces for the instrument in 1796. Gustav Mahler used the mandolin in his Symphony No. 7 and Symphony No. 8, and Igor Stravinsky included it in his ballet Agon.
Mandolin orchestras, known as Estudiantinas in Italy and Zupforchestern in Germany, consist of sections like first and second mandolins, mandolas, and mandocellos. These ensembles remain especially popular in Japan and Germany, but exist throughout the United States, Europe, and the rest of the world.