Oct. 12, 2012
-- It might look like just an ordinary picture of Stonehenge, but this is how the creators of the prehistoric monument wanted the site to be viewed, according to research using the latest 3D laser scanning technology. The groundbreaking analysis determined that the prehistoric monument was built to show off the solstices. In this view Stonehenge would look best when approaching from the Avenue, its ancient processional way to the north east.
Commissioned by the English Heritage, the laser-scan survey revealed in unprecedented detail the efforts made by prehistoric people at Stonehenge. "The result of the project were beyond all expectations. The investigation identified traces of stone working on virtually every stone," Marcus Abbott, head of geomatics and visualization at ArcHeritage, Hugo Anderson-Whymark, an Oxford-based expert on ancient worked stone, and colleagues wrote in the English Heritage report.
The laser-equipped researchers investigated the entire site. The laser scanner collected data with a resolution of 1 mm across the entire stone circle, and of just 0.5 mm for four stone surfaces of special interest. More than 700 surface features came to light.
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The laser highlighted prehistoric carvings from 4,500 years ago as well as damage made by modern visitors. Along with modern graffiti, this image shows scores of little axe heads and a possible dagger added when the slabs were already 1,000 years old.
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Overall, the laser scanning revealed 71 new Bronze Age axe heads, which bring the number of this type of carvings known at Stonehenge to 115.
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But the most interesting findings came from analysis of the stone surfaces. The study showed that the techniques and amounts of labor used varied from stone to stone. According to the researchers, these variations provide almost definitive proof that it was the intent of Stonehenge's builders to align the monument with the two solstices along a north-east/south-west axis. Indeed, the extremely straight and neat outline of the Great Trilithon, compared with all the other trilithons, shows that Stonehenge creators made deliberate efforts to shape it more carefully due to its special position on the solstice axis, just as they did for other stones that flank this axis.
The laser scanning showed that sides of the stones that flanked the solstice axis were most carefully worked to form very straight and narrow rectangular slots. To make them glisten in the sunlight, some stones had their crusts removed. These stones include two of the north-east facing sarsens in the outer circle, the Great Trilithon in the inner sarsen horseshoe, and an isolated upright stone in the south-west segment of the outer circle. By contrast, the stones in the south-western segment of the circle did not have their crusts removed.
The specially smoothed slabs created a dazzling light effect when the sun rays hit the stones. They would glisten in the dawn light on the longest day of the year and at sunset on the shortest This drawing shows Stonehenge in about 2300 B.C., after the construction of the sarsen outer circle and trilithons. Note the solstice axis.
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A short hosepipe may have solved one of the many mysteries of Stonehenge, showing that the iconic monument was once a perfect, complete circle.
Dry weather in summer 2013 at the Wiltshire monument revealed marks of parched grass in an area that had not been watered.
According to a report in the journal Antiquity, the patchmarks represent the position of the missing sarsen stones which once completed the Neolithic circle.
"Despite being one of the most intensively explored prehistoric monuments in western Europe, Stonehenge continues to hold surprises," English Heritage steward Tim Daw and colleagues wrote.
Located in the county of Wiltshire, at the center of England's densest complex of Neolithic and Bronze Age monuments, Stonehenge has been the subject of myth, legend and -- more recently -- scientific research for more than eight centuries.
The monument was likely built in several stages with "the unique lintelled stone circle being erected in the late Neolithic period around 2500 B.C.," according to the English Heritage.
Researchers have long investigated each part of the monument -- the massive central trilithons, the smaller bluestone settings, the sarsen circle capped by lintels, the outer bank and ditch -- debating whether the outer prehistoric stones were once completely round.
Indeed, the possibility that Stonehenge was an intentionally incomplete monument, with the sarsen circle only finished on the north-eastern side, has been suggested since the mid 18th century.
Now, a hosepipe too short to cover the outer part of the circle where no stones still stand, may have provided a definitive answer, revealing what excavations and high-resolution geophysical surveys failed to find.
Spotted by Daw, the patches on the ground -- believed to be "stone holes" -- appeared in the sarsen circle exactly where stones were expected to stand.
Such crop marks are produced when plants grow over features that have been buried in the ground for a long time, even long after they have been removed.
Buried or once-buried structures interfere with plant growth and develop at a different rate to those growing immediately adjacent. In this case, deep stone holes may have changed the earth permeability, affecting the grass growth.
"Plants that may have initially benefited from the easily available rooting and moisture in disturbed ground fail as the soil dries out, whilst the shorter-rooting surrounding plants manage to survive by extracting water directly from the porous chalk," Daw and colleagues wrote.
A survey, using Differential Global Positioning System equipment, was immediately undertaken, but unfortunately it suffered from limited time, given the elusive nature of the vanishing marks.
"Ideally the survey would have differentiated between marks caused by parching –- the majority -– and those caused by lusher growth," Daw and colleagues wrote.
"It would have also have graded the marks into 'definitive', 'probable' and 'possible' categories. This was not possible, and the result must therefore be treated with caution," they added.
English Heritage hopes to corroborate the findings with searching historic aerial photographs of the site and with future observation of the same phenomenon in similar weather conditions.