Final answer:
Antonio Vivaldi was initially employed as a violin instructor at the Ospedale della Pietà, composing and performing many important works that contributed to the Baroque era.
Step-by-step explanation:
Antonio Vivaldi, a distinguished composer and musician from the Baroque period, was initially employed by the Ospedale della Pietà, a Venetian institution known for its musical education, primarily as a violin instructor. Within this setting, he composed many of his major works and contributed to spreading the influence of the violin through his teachings and performances. While the violin was Vivaldi's primary instrument at the Pietà, his role there was multifaceted; he also composed orchestral and vocal music for the institution's all-female ensembles, further reinforcing the popularity and centrality of the violin in Baroque music.