music festivals, series of performances separate from the normal concert season and often, but not always, organized around an idea or theme. Music festivals usually are held annually in the summer, sometimes in the open air. The concept has been traced as far back as the sixth-century BC Pythian Games at Delphi, which included musical competitions. In the Middle Ages competitive festivals were sponsored by guilds. The eisteddfod in Wales is a direct descendant of medieval competitive festivals. Among the best-known music festivals with a specific theme held today are the Bayreuth Festival, which features the operas of Wagner; the Munich and Glyndebourne Festivals, which feature opera; the Darmstadt modern music festival; the Warsaw Autumn Days; England's Aldeburgh Festival, which was instituted by Benjamin Britten and concentrates on modern music; the Mostly Mozart festival in New York City; and the Newport Jazz Festival (now held in New York City and Newport). The Salzburg Festival began (musically) as a Mozart festival; today, however, other composers are also featured; it is perhaps the outstanding example of a general classical music festival. Similar events are held in New York City (notably Lincoln Center's Mostly Mozart Festival), Aspen, Colo. (see Aspen Music Festival), Edinburgh, Spoleto (see Spoleto Festival), and Bergen (Norway). The Tanglewood Music Festival in Lenox and Stockbridge, Mass., features the Boston Symphony. The festival idea has spread all over the world; Osaka began a festival of music and drama in 1958. Festivals of rock music have frequently been held on a one-time basis. Two of the most famous were the Monterey Pop Festival (1967) and Woodstock (1969).