How did Ludwig van Beethoven substantially alter the Classical symphony form of Haydn and Mozart?

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Beethoven used the motif (a short, recurring musical element) to expand and unify the symphony structure, which was a departure from the more straightforward structure of Haydn and Mozart's symphonies. Beethoven did not eliminate the fourth movement, selectively reduce the number of instruments, or emphasize classical simplicity.

How Did Ludwig Van Beethoven Substantially Alter the Classical Symphony