Final answer:
Ludwig van Beethoven's contributions transitioned the Classical to the Romantic era, making his legacy the most enduring and influential of the nineteenth century's composers.
Step-by-step explanation:
The nineteenth century saw a flourishing of musical creativity that led to lasting and influential legacies. Among the composers of this period, Ludwig van Beethoven stands out for his overwhelming influence. He bridges the Classical and Romantic eras, with his later works embodying the essence of Romanticism.
Both during the Romantic era and into the post-Romantic era, composers like Mahler and Strauss explored nationalistic music and stretched Romantic techniques to their limits. Meanwhile, modernists like Igor Stravinsky signaled the move towards new musical expressions. However, if we consider the total words 180 in the Romantic period's substantial legacy, it's clear that Beethoven's impact was the most enduring and far-reaching.
Beethoven's late works, including his symphonies and sonatas, have remained staples in concert halls worldwide. They reflect a transition from the order and harmony of the Classical tradition to the emotive and expressive character of the Romantic aesthetic. His innovations in musical form and harmony laid the groundwork for future composers, making his legacy a central pillar in Western classical music's development.