I want to know the answer to the following question:
What did not exist through the entire classical music period?
All the background I'm provided with is that "Given the wide range of styles in classical music, from Medieval plainchant sung by monks to Classical and Romantic symphonies for orchestra from the 1700s and 1800s to avant-garde atonal compositions for solo piano from the 1900s, it is difficult to list characteristics that can be attributed to all works of that type.". Is that enough to answer the question?
Answer: no