symphony, a lengthy form of musical composition for orchestra, normally consisting of several large sections, or movements, at least one of which usually employs sonata form (also called first-movement form). Symphonies in this sense began to be composed during the so-called Classical period in European music history, about 1740–1820. The early part of this period and the decade immediately preceding it are sometimes called pre-Classical, as are the symphonies written before about 1750. During the 19th century, which included the Romantic period, symphonies grew longer, and composers concerned themselves with ways of unifying the movements; extramusical programs and new approaches