Piano sonatas (Beethoven)
Ludwig van Beethoven wrote his 32 piano sonatas between 1795 and 1822. Although originally not intended to be a meaningful whole, as a set they compose one of the most important collections of works in the history of music. Hans von Bülow called them "The New Testament" of the piano literature (Johann Sebastian Bach's "The Well-Tempered Clavier" being "The Old Testament").
String Quartets Nos. 1–6, Op. 18 (Beethoven)
Ludwig van Beethoven's Op. 18, published in 1801 by T. Mollo et Comp in Vienna in two books of three quartets each, consisted of his first six string quartets. They were composed between 1798 and 1800 to fulfill a commission for Prince Joseph Franz Maximilian Lobkowitz, who was the employer of Beethoven's friend, the violinist Karl Amenda. They are thought to demonstrate his total mastery of the classical string quartet as developed by Joseph Haydn and Wolfgang Amadeus Mozart. The order of publication (numbering within the opus) does not correspond to the order of composition. Beethoven composed these quartets in the sequence 3, 1, 2, 5, 4, 6. See: