Stonehenge was an assemblage of giant stones erected in Wiltshire during the 2nd Millennium BC. John Brent had a theory that Stonehenge was in reality an ancient spaceport. (PROSE: Time and Relative) In fact, he wasn't too far off from the truth — Stonehenge served as the burial site and hiding place of the Pandorica, an ancient box used by the Alliance to trap the Eleventh Doctor. They used the shape itself of the rocks as a huge transmitter to send over the members of the Alliance should the Doctor come to call. (TV: The Pandorica Opens)
The Eighth Doctor and Samantha Jones visited Stonehenge while it was being constructed. (PROSE: The People's Temple) The Monk claimed to have used anti-gravity lifts to assist in the completion of Stonehenge. (TV: The Time Meddler)
At some point in its history, the Alliance placed the Pandorica beneath Stonehenge for the Eleventh Doctor to find. The pillars beneath Stonehenge began to act as a transmitter for the members of the Alliance to converge on it in 102. The transmission was sent to everyone and to all time zones, resulting in Vincent van Gogh (presumably amongst others) having visions of the opening of the Pandorica. When the Doctor arrived at Stonehenge and found the Pandorica, the Alliance imprisoned him within it. (TV: The Pandorica Opens)
During the times of the druids, Cybermen were believed to have been guarding the Pandorica underneath Stonehenge. Parts of Cybermen such as arms and heads lay on the ground around the henge. The Doctor believed they had been 'dusted up by the locals'. (TV: The Pandorica Opens) Since the Doctor altered the timeline, the presence of the Pandorica and, subsequently, the Cybermen had never occured. (TV: The Big Bang)
THE Stonehenge SPEECH
Before the sealing of the Doctor in the Pandorica, the Doctor assumed the Pandorica was already occupied and gave a speech to the assembled Alliance at Stonehenge.
"Hello Stonehenge! Who takes the Pandorica takes the universe. But, bad news everyone, 'cause guess who?! Ha! Listen, you lot, you're all whizzing about, it's really very distracting. Could you all just stay still a minute because I - am - talking! Right. Now the question of the hour is: Who's got the Pandorica? Answer: I do. Next question. Who's coming to take it from me? Come on! Look at me! No plan, no backup, no weapons worth a damn. Oh, and something else, I haven't got anything to lose. So if you're sitting up there in your silly little spaceships with all your silly little guns, and you've got any plans on taking the Pandorica tonight, just remember who's standing in your way. Remember every black day I ever stopped you, and then - and then! do the smart thing. Let somebody else try first."
The speech turned out to be completely based off the wrong premise, as the Pandorica was opening so it could be occupied, not be stolen.
In either November or December 1967, one of the stones of the monument had "a circular symbol with an 'R' in it" — the symbol of the Revolution Man — carved into it over night. (PROSE: Revolution Man)