After finally returning with his father from Italy on 13 March 1773, Mozart was employed as a court musician by the ruler of Salzburg, Prince-Archbishop Hieronymus Colloredo. The composer had many friends and admirers in Salzburg and had the opportunity to work in many genres, including symphonies, sonatas, string quartets, masses, serenades, and a few minor operas. Between April and December 1775, Mozart developed an enthusiasm for violin concertos, producing a series of five (the only ones he ever wrote), which steadily increased in their musical sophistication. The last three—K. 216, K. 218, K. 219—are now staples of the repertoire. In 1776, he turned his efforts to piano concertos, culminating in the E concerto K. 271 of early 1777, considered by critics to be a breakthrough work.