Final answer:
The proscenium stage format was most prominently realized in the Victorian era, a time when melodrama was immensely popular and when the theatrical culture of the time was well-suited to the proscenium's 'framing' of performances.
Step-by-step explanation:
The proscenium stage format reached its highest realization in the Victorian era. During this time, melodrama became the prevalent form of theatre and was at the peak of its popularity in the 1840s. Characteristics of melodrama, such as music to enhance emotional impact, moral simplicity, and spectacular special effects, were well-suited to the proscenium stage, which separated the audience from the performance with a 'picture frame'.
The Victorian era continued the tradition of lavish theatre productions that catered to an expanding middle class, yearning for entertainment and drama. The proscenium arch provided a clear division between spectators and performers, fostering an ideal environment for the melodramatic performances popular at the time.
Additionally, the era witnessed numerous touring troupes across America, performing a variety of shows from classical Shakespeare to vaudeville acts, which further signified the era's affinity for theatre.