The Well-Tempered Clavier

In Weimar, Bach continued to play and compose for the organ and perform concert music with the duke's ensemble. He also began to write the preludes and fugues which were later assembled into his monumental work The Well-Tempered Clavier ("clavier" meaning clavichord or harpsichord), consisting of two books, each containing 24 preludes and fugues in every major and minor key.