The oldest is the U.S. Open. It began as the Western Open in 1900, held in Minnesota. It is the "congress" of US Chess – the annual meeting of the Delegates is held concurrently, as well as many smaller gatherings and events. Several hundred players participate (the highest number, 836, was at the 1983 event in Pasadena). Five invitational events are held concurrently. Each US Chess state affiliate nominates a representative to each of the five invitationals. The five invitationals are: The National Tournament of Senior State Champions (50+), The GM Arnold Denker National Tournament of High School State Champions (9-12), The Dewain Barber National Tournament of Middle School State Champions (6-8), The John D. Rockefeller National Tournament of Elementary School State Champions (K-5), and The Ruth Haring National Tournament of Girls State Champions (K-12). Players generally qualify for these events by winning a state championship tournament, although each state affiliate is allowed to use any criteria for selecting its representatives.