Stonehenge had a previously unknown wooden "twin" just 900m to its north-west, according to remarkable new archaeological investigations.
Using the ground-penetrating equivalent of an X-ray, scientists have discovered what appears to have been a circle of massive timber obelisks, constructed more than 4,200 years ago.
The newly discovered "henge" would have been visible from Stonehenge itself – and seems to have been part of a wider prehistoric ritual and religious landscape. Roughly 25m in diameter, it was almost the same size as the central part (the circle of standing stones) at Stonehenge itself.
The newly discovered monument – almost certainly some sort of Neolithic temple – is thought to have consisted of 24 wooden obelisks, each around 75cm in diameter and therefore potentially up to 8m high. The circle of obelisks was enclosed by an inner ditch and probable outer bank.
Of potential significance is the fact that the newly found henge "mirrors" a similar monument (this time long known to archaeologists) on the other side of Stonehenge – 1,300m south-east of the famous monument. Like the newly discovered site, it is in direct line of sight of Stonehenge and had two entrances. All three monuments would have been roughly aligned.
The discovery of the site north-west of the stone circle suggests that the Stonehenge landscape was even more complex than people have thought – and archaeologists are now keen to find further unknown elements of it.
The archaeologists – from Birmingham, Bradford, St Andrews and Vienna Universities – are trying to map the unknown aspects of the Stonehenge landscape without digging a single hole.
Instead of conventional excavations, they are using X-ray-style systems which look beneath the ground surface. The techniques – including magnetometry, ground-penetrating radar, electrical imaging and resistivity – are likely to yield huge amounts of previously unknown information about what the Stonehenge landscape looked like 40 to 50 centuries ago.
Over the next four years the survey, led by Professor Vince Gaffney of Birmingham University's Institute of Archaeology and Antiquity, is likely to produce hundreds of millions of pieces of information from 14 sq km of countryside which will then be collated and analysed to produce a detailed map.
"Some 90 per cent of the Stonehenge landscape is still terra incognita. Our survey will hopefully begin to remedy our current lack of knowledge," explained Professor Gaffney. "The discovery will significantly change the way we think about the landscape around Stonehenge."
The newly discovered prehistoric temple was found using the subsurface archaeological detection system known as magnetometry, which measures the differences in interaction with the Earth's magnetic field produced by different layers or deposits of earth or rock.
Detecting variations in the strength of the magnetic field revealed the existence of the enclosure ditches and the pits believed to have held the timber obelisks at the newly discovered henge.