An oratorio is a large musical composition for orchestra, choir, and soloists. Like most operas, an oratorio includes the use of a choir, soloists, an instrumental ensemble, various distinguishable characters, and arias. However, opera is musical theatre, while oratorio is strictly a concert piece – though oratorios are sometimes staged as operas, and operas are sometimes presented in concert form. In an oratorio, the choir often plays a central role, and there is generally little or no interaction between the characters, and no props or elaborate costumes. A particularly important difference is in the typical subject matter of the text. Opera tends to deal with history and mythology, including age-old devices of romance, deception, and murder, whereas the plot of an oratorio often deals with sacred topics, making it appropriate for performance in the church. Catholic composers looked to the lives of saints and histories from the Bible while Protestant composers only to Biblical topics. Oratorios became extremely popular in early 17th-century Italy partly because of the success of opera and the Catholic Church's prohibition of spectacles during Lent. Oratorios became the main choice of music during that period for opera audiences.