Britain’s favourite monument is stuck in the middle of a bad-tempered row over road traffic. By Charlotte Higgins

Stonehenge, with the possible exception of Big Ben, is Britain’s most recognisable monument. As a symbol of the nation’s antiquity, it is our Parthenon, our pyramids – although, admittedly, less impressive. Neil MacGregor, the former director of the British Museum, recalls that when he took a group of Egyptian archaeologists to see it, they were baffled by our national devotion to the stones, which, compared to the refined surfaces of the pyramids, seemed to them like something hastily thrown up over a weekend.

Unlike those other monuments, though, Stonehenge is more or less a complete mystery. Nobody knows for sure why, or by whom, this vast arrangement of boulders was erected on Wiltshire’s downlands, in the south of England, about 5,000 years ago. Into this void have rushed myriad theories, from the academically sober to the blatantly fantastic. Over the centuries, its construction has been confidently credited to giants, wizards, Phoenicians, Mycenaeans, Romans, Saxons, Danes and aliens. (According to one medieval theory, Merlin had it transported from Ireland to serve as the funeral monument for Britons slaughtered by Hengist, the treacherous Saxon.)