Mozart's first string quartet, K.80 in G, was completed at an inn in the northern Italian village of Lodi on 15 March 1770, ‘at 7 o'clock in the evening’ according to an annotation on the autograph manuscript. In a letter of 24 March 1778 Mozart reminded his father of the piece, and explained that he had arranged for copies of it to be made for Baron Otto Heinrich von Gemmingen-Homberg (1753–1836), a government official in Mannheim. Between 13 December 1769 and 28 March 1771 Mozart and his father were on tour in Italy. For Wolfgang this was a period of invaluable exposure to Italian operatic styles which bore fruit in commissions to compose two operas for Milan: Mitridate, re di Ponto (first performed on 26 December 1770) and the serenata, Ascanio in Alba (17 October 1771), to celebrate the marriage of Archduke Ferdinand. The Mozarts made a second journey (to supervise arrangements for Ascanio) between (mid?) August and 15 December 1771, and a third (24 October 1772 to 13 March 1773) to attend rehearsals for Lucio Silla.

During these Italian visits Mozart encountered such diverse personalities as Giovanni Battista Sammartini (c. 1700–1775) and Padre Giovanni Battista Martini (1706–84), major figures in eighteenth-century Italian composition and musical theory. Leopold recalls a meeting with the former in a letter from Milan dated 10 February 1770: ‘It would take too long to describe in detail the evidence of his knowledge which Wolfgang has given in the presence of Maestro Sammartini and a number of the most brilliant people, and of how he has amazed them’.