Stonehenge sunrise from English Heritage (2020)
Here is the abstract from Nash et al. (2020):
“The sources of the stone used to
construct Stonehenge around 2500 BCE have been debated for over four centuries.
The smaller “bluestones” near the center of the monument have been traced to
Wales, but the origins of the sarsen (silcrete) megaliths that form the primary
architecture of Stonehenge remain unknown. Here, we use geochemical data to
show that 50 of the 52 sarsens at the monument share a consistent chemistry
and, by inference, originated from a common source area. We then compare the
geochemical signature of a core extracted from Stone 58 at Stonehenge with
equivalent data for sarsens from across southern Britain. From this, we
identify West Woods, Wiltshire, 25 km north of Stonehenge, as the most probable
source area for the majority of sarsens at the monument.”
The story of how samples from the
Stonehenge sarsens, were obtained for analysis is an interesting one in itself.
From Nash et al. (2020) again:
“During a restoration program at
Stonehenge in 1958, three sarsen stones that fell in 1797 were re-erected
(uprights 57 and 58 and lintel 158 from the Trilithon Horseshoe.. In the course
of this work, longitudinal fractures were noted through Stone 58. After re-erection,
to conserve the integrity of the upright, three horizontal holes were drilled
through the full thickness of the stone by Van Moppes Ltd. Metal ties were
inserted into these holes and secured using recessed metal bolt heads, with the
holes at the surface of the upright filled using plugs of sarsen.
The drill cores from Stone 58
were assumed “lost.” However, in 2018, one complete (1.08 m long, 25-mm
diameter) but fragmented core was returned to the United Kingdom from the
United States by Robert Phillips, a former employee of Van Moppes who was on-site
during the drilling operations.”
It was this core that was used in
the chemical analysis plus data collected by non-destructive testing of the
other sarsen stones at Stonehenge. Basically they the scientists measured the
Zr/trace element ratios to produce geochemical signatures for each of the 20
sarsen sampling areas that they thought the huge boulders might come from.
The result was that only one site
gave an exact match. This was the sample of a boulder from West Woods,
Wiltshire about 25km away.
As the largest sarsen is about
9.1m high, and weighs about 30 metric tons just how did ancient man 4,500 years
ago transport these immense boulders to Stonehenge? Plausible routes were suggested
by Nash et al. (2020): a completely overland route taking a western path (dashed
route at left on the diagram below) or a partly overland route followed by use
of the River Avon to the east.
Possible routes of transportation
of the sarsen stones form source Stonehenge. Adapted from Nash et al. (2020)
Fig. 1.
Whichever route it was, it must
have been a huge undertaking, involving the whole community over generations.
References
English Heritage (2020) at: https://www.english-heritage.org.uk/visit/places/stonehenge/history-and-stories/
accessed 30.07.20
Nash, D. J. et al. (2020). Origins of the sarsen megaliths
at Stonehenge. Science Advance Vol. 6, no. 31, eabc0133. DOI:
10.1126/sciadv.abc0133
