Wolf Trap Farm in Virginia, maintained by the National Park Service, is one of the nation's large open-air centers where music festivals are held. Such festivals began in this country in the mid-19th century, although the Handel and Haydn Society of Boston presented concerts in that city since 1815. Summer festivals now form an important and permanent aspect of musical life, completing what has become a 12-month musical season. An estimated more than 300 such summer festivals are found in the United States.