A string quartet is a musical ensemble consisting of four string instruments: two violins, a viola, and a cello. This format became popular during the Classical period, with composers like Joseph Haydn and Wolfgang Amadeus Mozart significantly contributing to its repertoire. String quartets are known for their rich harmonies and intricate interplay between the instruments. The structure of a typical string quartet includes several movements, often following a fast-slow-fast pattern. Each instrument plays a distinct role, with the first violin usually leading the melody while the others provide harmony and depth. This combination allows for a wide range of emotional expression and musical exploration.