FACTBOX: A few facts about Glastonbury festival

(Reuters) - Glastonbury is the world’s biggest open air arts and music festival, and covers 900 acres in the mystical Vale of Avalon, where legend claims King Arthur was buried, Joseph of Arimathea walked and where leylines converge.

The festival is notorious for its torrential rain after three ‘washout’ years in 1997, 1998 and 2005 in which the entire festival site on Michael Eavis’s Worthy Farm, deep in southwest England, became a slippery quagmire. Some fans revel in the mud.

The big lure this year is the hot line-up of bands, including rock legends The Who, The Killers from Las Vegas, the Arctic Monkeys, and Canada’s Arcade Fire, at a three-day event that has poetry, theatre, circus and comedy.

In previous years performers have included such famous names as Paul McCartney, Rod Stewart, David Bowie, Tom Jones and Robbie Williams.

The first festival was held in September 1970 over a two day period with acts including Marc Bolan, Keith Christmas, Stackridge and Al Stewart. 1,500 attended with admission being just one pound - but that included free milk from the farm.

In 1971 the festival moved to the time of the Summer Solstice and was known as the “Glastonbury Fayre”. It was paid for by supporters of the ideal so the entrance was free and took a medieval tradition of music, dance, poetry, theatre, lights and spontaneous entertainment. The first “pyramid” stage was constructed out of scaffolding and expanded metal covered with plastic sheeting, built on ancient Glastonbury-Stonehenge ley line. Acts included Hawkwind, Traffic, Melanie, David Bowie, Joan Baez and Fairport Convention watched by an estimated 12,000.

In 1981 the name was changed to the Glastonbury Festival and the decision was taken to build a new permanent Pyramid stage which doubled as a cowshed and animal feed store during the winter months. Early festivals were closely linked to the Campaign for Nuclear Disarmament, and during the 1980s organizers had to seek licenses following the introduction of a local government act to regulate such events.

In 1985 the size of the site was increased by 100 acres as neighboring Cockmill farm land was purchased and the steadily increasing attendance figure saw 40,000 revelers.

1990 saw clashes between security teams and travelers which resulted in 235 arrests and became known as the Battle of Yeoman’s Bridge. 1992 saw 250,000 pounds ($498,100) of donations to Greenpeace and Oxfam as organizers shifted the emphasis away from nuclear disarmament with the end of the Cold War. The 1998 festival broke the 100,000 attendance mark despite a second year of quagmire conditions.

The 2005 festival featured 385 live performances and was attended by around 150,000 people.

The festival has been an annual fixture since 1981, albeit with breaks in 1988, 1991, 1996, 2001 and 2006.