The Romantic period represented an expansion of structure and expression in European classical music from the early 19th century to the early 20th century. For all of its departures from the style of the Classical period, it maintained many of the same characteristics.
According to "The Harvard Dictionary of Music," Romantic and Classical era music are merely phases within a continuum of development. There is more continuity than change.
Romantic era composers appreciated classical form. Romantic artists continued to write operas, symphonies and concertos, all accepted classical forms.
Romantic composers like Schubert, Brahms and Mendelssohn produced Classical style chamber music, music intended for small ensembles, during the late Romantic era.
Harmony and Melody
According to the "Billboard Illustrated Encyclopedia of Classical Music," aspects like harmony and melody were not destroyed by the Romantic period, but merely expanded upon.
Ludwig van Beethoven
Ludwig van Beethoven bridged the gap between the two forms. His early compositions were in the Classical style, while his later compositions, like the "Moonlight Sonata" are considered Romantic.