THEY don’t look terribly exciting. Who would get worked up about some gnarly
old timbers in an ancient peat bog? But these aren’t just any old lumps of wood.
They are the remains of posts that supported an Iron Age walkway built almost
2500 years ago and used, it would appear, by the Druids of eastern England as a
platform from which to consign sacrificial objects to the watery depths. All
across northern Europe, people made offerings such as swords, shields, tools,
boats and even humans. And while we still have little idea of why they offered
up these sacrifices, this particular walkway may give us an extraordinary
insight into their knowledge of the world around them.
These old oak posts suggest that the people who built the walkway were able
to predict lunar eclipses—or at least that’s the theory of a pair of
archaeologists from Sheffield University. It’s well known that the Moon had
practical and ritual significance in Iron Age times. But this is the first
inkling that any prehistoric peoples possessed such detailed knowledge of lunar
cycles.
The story begins in 1980, when a farmer saw posts jutting from the side of a
drainage canal in a field outside the village of Fiskerton in Lincolnshire, near
the River Witham. Thinking the wood looked old, he fetched his metal detector.
The site was close to where the famous Witham Shield—a fine example of
Celtic bronze craftsmanship now in the British Museum—had been discovered
in the 18th century, so when the farmer dug up an ancient sword hilt, it looked
as though he might have struck a rich vein of archaeological remains. The hilt
dated from 350 BC, and when the site was professionally excavated by Naomi Field
it yielded a further 270 metal objects, including swords, spearheads and
hammers. She also uncovered a piece of skull with a fresh sword cut on the
back.
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There seems little doubt that this was an ancient ritual site. Nobody lived
here in the Iron Age—it was a swamp—but people did have access to
the watery wasteland. Besides the votive objects, the archaeologists found many
large timbers which appeared to have come adrift from a walkway. The boardwalk
had been supported on two parallel rows of tall posts, most made of oak. These
are key to the next stage in the story.
The excavated area contained 150 posts in 12 clusters, but it was apparent
that the two rows of uprights extended beyond the confines of the dig, both to
the north and south. Tree-ring analysis by Jennifer Hillam, then at Sheffield
University, revealed that the clusters were the result of new posts being added
in roughly the same place every 18 years or so. More recently,
dendrochronologists have used the characteristic patterns of growth rings to
discover exactly when the trees were cut down. The 44 posts dated so far suggest
there were 12 renewal events between 457 and 339 BC. All the trees were felled
in winter.
Archaeologists Andrew Chamberlain and Mike Parker Pearson from Sheffield
University returned to the site last year. In an attempt to find an astronomical
connection for the 18-year intervals, Chamberlain visited a NASA website that
documented solar and lunar eclipses. He was surprised to find that five of the
12 years when posts were replaced coincided with years in which there was a
total lunar eclipse in the middle of winter—just when the trees had been
cut.
A lunar eclipse occurs during a full Moon when Earth’s shadow falls on the
Moon. Variations in the orbits of the Moon and Earth mean that although eclipses
do not often occur at the same time and in the same place in the sky, they do
follow regular patterns. A complete cycle, when the relative positions of the
Sun, Moon and Earth return to approximately the same starting points, generates
a run of different eclipses. Its end is marked by an eclipse at almost exactly
the same time and place as the first one. The two matching eclipses occur 18
years and 11.3 days apart.
In the 18th-century, astronomer Edmond Halley called this succession a Saros
cycle, from the Babylonian word for repetition. At any one time there are
several Saros cycles in action—two are responsible for midwinter eclipses
in Iron Age Britain. Three of the dates when posts were felled coincide exactly
with eclipses associated with one of these cycles: the winters of 447/6, 375/4
and 339/8 BC; two others, in 440/39 and 422/1 BC, fit with the second.The
Sheffield archaeologists say it’s highly improbable that these matches are due
to chance, and have put this claim on a firm statistical footing. “The
chi-squared tests indicate less than 1 chance in 1000 that this pattern is
insignificant,” says Parker Pearson. “I’d go to the bookmakers on that.”
All but the two posts cut down in winter 385/4 BC—which are not
actually part of the track—can be related to eclipses in one or other of
these cycles, if it is allowed that trees might have been felled and collected
up to two years before being used to revamp the trackway. The idea that eclipses
were being predicted—and that the trackway was being rebuilt in
anticipation of the event—is reinforced, say Chamberlain and Parker
Pearson, by the fact that totality of two of the eclipses coinciding with
trackway building (440/39 and 386/5 BC) wouldn’t have been visible in
Lincolnshire as they occurred when the Moon was below the horizon. What’s more,
only the Saros winter eclipses were matched by trackway renovation.
The archaeologists admit the fit is not perfect, but are going public in the
hope that others might have further insights. “We’re happy to be proved wrong,”
says Chamberlain, “but we’d like people to look for similar evidence at other
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Already the critics are having their say. “The argument is not as good as it
first appears,” Clive Orton, an archaeologist and statistician at University
College London, told Â鶹´«Ă˝. He says the Sheffield pair have
used the wrong statistical test, and that an alternative—an exact binomial
test—would be more appropriate. His analysis gives a 1 in 100 chance that
the pattern is purely accidental—a lower level of significance, but one
that he still thinks calls for an explanation.
Orton doesn’t totally dismiss the suggestion that Iron Age people might have
noticed the periodicity of the eclipses. But equally, he says, the apparent
pattern could have other origins. He compares Iron Age track building to repairs
on his local railway. “Men replace sleepers every few years on my line,” he
says. And while the repairs are unlikely to occur randomly, they are not, as far
as he knows, timed by lunar divination.
To Iron Age people, a total lunar eclipse would certainly not have gone
unnoticed. Full Moons would have been a significant light
source—particularly in winter when the nights are long—and everyone
would have been familiar with the Moon’s phases and movements. But were they
also using eclipses to provide a ritual calendar? Elsewhere, ancient Babylonian
clay tablets show that their astronomers recognised the Saros cycle sometime
before 500 BC—though when the Babylonians learned to predict eclipses is
still uncertain. The ancient British could have had similar insights, even
though they couldn’t record them in writing. “There could have been an oral
tradition, recording observations in verse,” says Chamberlain.
Evidence of systematic lunar observations in late Iron Age Europe comes from
two calendars engraved onto fragments of bronze sheets found 30 kilometres apart
at Coligny and Villards-d’Héria in eastern France. These divide months
according to the brightness of the Moon, and record them as either “good” (30
days) or “bad” (29 days). The sheets, which originally measured 1 by 2 metres,
are thought to date from around AD 200. Although engraved with Roman script, the
language is Celtic, and the system is quite different from the solar scheme
introduced by Julius Caesar in the 1st century BC, suggesting the calendars have
more ancient origins.
The French calendars mark time by counting in nights. Caesar himself noted:
“In celebrating birthdays, the first of the month and the start of a year, [the
Gauls] work on the principle that night comes first and is followed by day.”
Other Classical writers support Caesar’s implication that late prehistoric
northern Europeans were competent astronomers. In the first century AD, Pliny
the elder describes them as “holding long discussions about heavenly bodies . .
. and the size of the Universe”. Elsewhere he wrote: “It is by the Moon that
[the Druids] measure their months and years.”
Andrew Fitzpatrick of the consultancy Wessex Archaeology describes the
thinking of these peoples as “closer to modern astrology than modern astronomy”.
But this, he argues, lends weight to Chamberlain and Parker Pearson’s theory.
That eclipses may not all be precisely marked at Fiskerton is not important,
according to Fitzpatrick. “They are trying to respect the cycle as best they
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Last summer, archaeologists were back at the site for a new excavation, in
advance of drainage works on the Witham. As before, they found many metal
artefacts. They also recovered an Iron Age dugout canoe, pegged down and unused,
suggesting that it, too, was a ritual offering. And there, again, crossing the
archaeologists’ trench from north to south, were the two rows of posts. One of
them branched into a third row just before they vanished back into unexcavated
peat.
Sheffield University’s Ian Tyers will be examining growth rings on these
newly unearthed timbers with particular care. Will they strengthen the Saros
hypothesis by showing that new posts were added in more of the eclipse years? Or
will they tip the balance against it, with dates all over the place? If the tree
rings don’t deliver, there’ll be a new sacrifice in the bog—the carefully
computed theory of two British archaeologists.
