What are the three periods of Ludwig van Beethoven’s musical career?

Ludwig van Beethoven’s musical career, which bridged the transition between the Classical and Romantic eras, is generally divided into three distinct periods:1

• First Period (1794–1800): During this time, Beethoven’s work remained largely within the bounds of traditional 18th-century techniques and ideas. He focused heavily on compositions for the piano, though he also produced works such as the First Symphony and various string quartets and trios.12
• Second Period (1801–1814): This was Beethoven’s most prolific era, characterized by an increased use of improvisatory material. Many of his most famous works were composed during these years, including the Eroica Symphony (1805), Symphony No. 5 in C Minor (1808), Symphony No. 6 in F Major (1808), and Symphony No. 7 in A Major (1813).1
• Third Period (1814–1827): This final phase of his career is noted for featuring a wide range of complex musical harmonies and textures.1