"They literally trampled down the fence and ran into the stones, jumping over them, sitting on top, hurling all sorts of objects at police," said a spokeswoman for Wiltshire police in southwest England. "They were throwing all kinds of things and we believe there has been some damage to the stones themselves," she said.
There is a history of violent clashes between police and New Age travelers, whose alternative lifestyle often leads to mass congregations at summer festivals, ecological protests and anti-authority demonstrations.
The travelers have been angered by tough new laws that enable police to crack down on mass gatherings in the name of maintaining public order. They believe police use the laws to victimize them and punish them for leading a non-conformist life.
The storming of the circle, which had been signaled in underground magazines and on the internet, prevented druids from celebrating the Summer Solstice, the time at which the sun strays farthest from the equator.
"There's a disappointment and also a great sadness," Emma Restell-Orr, joint chief druid of the British Order of Druids, told BBC radio. "The greatest sadness is perhaps seeing people standing and dancing on top of the stones. It's not only dangerous for them, it's desecration of a sacred site."
Druids, a pre-Christian religion of the Celts, have long been drawn to Stonehenge, one of a number of prehistoric monuments on Salisbury Plain. Dating from about 2800 BC, the site originally consisted of a circle of upright stones, linked by lintels, and an altar stone facing the rising sun.