WWE Pay-Per-View is a continuation of the weekly wrestling shows which generally build up to this monthly event. Expect it to be bigger, better, and more entertaining than the weeknight shows over three hours of television. WrestleMania is held in late March or early April; if it is held in April, then no pay-per-view is produced in March. With the exception of WrestleMania, each event is scheduled for three hours, although they usually run short of that time. Pay-per-view events are a significant part of the revenue stream for WWE. Many WWE pay-per-views are thematic, centered around particular types of matches, or have an annually-recurring main-event. Most themed pay-per-view-events (sans The Big Four) are roughly treated like filler themed events to carry the audience until the next event dating back to the days when the In Your House system was used.