About 20,000 people have celebrated the summer solstice at Stonehenge, an ancient circle of giant stones in southern England.

Revelers, spiritualists and others clad in antlers, black cloaks and oak leaves gathered at the prehistoric monument early Thursday. They came to welcome the sunrise on the longest day of the year in the northern hemisphere.

Stonehenge was built about 5,000 years ago, but its purpose remains a mystery.

One of Britain's most popular tourist attractions, Stonehenge is also the spiritual home for thousands of Druids, who practice ancient pagan rites dating back to Celtic Britain.

Although the monument remains open to the public, police closely monitor the site at solstice dates after violent clashes with revelers in the 1980s.

Some information for this report was provided by AFP and AP.