Final answer:
Mahler's Symphony No. 1 was originally a symphonic poem that was later expanded into a full symphony, reflecting the Romantic era's emphasis on emotional expression in music.
Step-by-step explanation:
Mahler's Symphony No. 1 started out as a symphonic poem and became a full symphony. Initially, it was conceived as a single-movement piece but was later expanded into a full four-movement symphonic work. This transformation is an example of how Romantic music often expressed the powerful drama of human emotion in various forms, from anger and passion to quiet passages of pleasure and joy, characteristic of composers from this era who aimed to connect deeply with listeners.