ROb: From Wikipedia:
The music of the Classical Period (1750 A.D. to 1830 A.D.) looked to the art and philosophy of Ancient Greece and Rome, to the ideals of balance, proportion and disciplined expression. It has a lighter, clearer and considerably simpler texture, and tended to be almost voicelike and singable. New genres were discovered. The main style was the homophony,[20] where prominent melody and accompaniment are clearly distinct.
Importance was given to instrumental music. It was dominated by further evolution of musical forms initially defined in the Baroque period: the sonata, the concerto, and the symphony. Others main kinds were trio, string quartet, serenade and divertimento. The sonata was the most important and developed form. Although Baroque composers also wrote sonatas, the Classical style of sonata is completely distinct. All of the main instrumental forms of the Classical era were based on the dramatic structure of the sonata.
One of the most important evolutionary steps made in the Classical period was the development of public concerts. The aristocracy would still play a significant role in the sponsorship of musical life, but it was now possible for composers to survive without being its permanent employees. The increasing popularity led to a growth in both the number and range of the orchestras. The expansion of orchestral concerts necessitated large public spaces. As a result of all these processes, symphonic music (including opera, ballet and oratorio) became more extroverted.
The best known composers of Classicism are Carl Philipp Emanuel Bach, Christoph Willibald Gluck, Johann Christian Bach, Joseph Haydn, Wolfgang Amadeus Mozart, Ludwig van Beethoven and Franz Schubert. Beethoven and Schubert are also considered to be composers in evolution towards Romanticism.
Romantic Music (c. 1810 A.D. to 1900 A.D.) turned the rigid styles and forms of the Classical era into more passionate and expressive pieces. It attempted to increase emotional expression and power to describe deeper truths or human feelings. The emotional and expressive qualities of music came to take precedence over technique and tradition. Romantic composers grew in idiosyncrasy, and went further in the syncretism of different art-forms (such as literature), history (historical figures), or nature itself with music. Romantic love was a prevalent theme in many works composed during this period. In some cases the formal structures from the classical period were preserved, but in many others existing genres, forms, and functions were improved. Also, new forms were created that were deemed better suited to the new subject matter. Opera and ballet continued to evolve.[17]
[17]
There’s a lot in here, but I bolded the two most important lines.