Article: Although professional wrestling started out as petty acts in sideshows, traveling circuses and carnivals, today it is a billion-dollar industry. Revenue is drawn from live event ticket sales, network television broadcasts, pay-per-view broadcasts, personal appearances by performers, branded merchandise and home video. Particularly since the 1950s, pro wrestling events have frequently been responsible for sellout crowds at large arenas, including Madison Square Garden, as well as football stadiums, by promotions including the WWE, the NWA territory system, WCW, and AWA. Pro wrestling was also instrumental in making pay-per-view a viable method of content delivery. Annual shows such as WrestleMania, SummerSlam, Royal Rumble, and formerly Bash at the Beach, Halloween Havoc and Starrcade are among the highest-selling pay-per-view programming each year. In modern day, internet programming has been utilized by a number of companies to air web shows, internet pay-per-views (iPPVs) or on-demand content, helping to generate internet-related revenue earnings from the evolving World Wide Web.

Question: what wrestling shows occur yearly?
WrestleMania, SummerSlam, Royal Rumble, and formerly Bash at the Beach, Halloween Havoc and Starrcade