The era with the largest orchestras was primarily the late Romantic period, transitioning into the early 20th century. During this time, particularly in the late 19th century and early 20th century, composers like Gustav Mahler, Richard Strauss, and Igor Stravinsky wrote works that called for large orchestral forces.
Mahler's symphonies, for example, often required extensive instrumentation, including expanded woodwinds, brass, percussion, and strings. Orchestras could sometimes number over 100 musicians for a single performance.
This trend towards larger orchestras was also influenced by the increasing complexity of orchestral music and the desire for a richer, fuller sound, which became a hallmark of the Romantic style. While modern orchestras vary in size depending on the repertoire being performed, the late Romantic and early 20th century period remains notable for the sheer scale of orchestral forces.