A Staff Report from the Straight Dope Science Advisory Board

What's the real story on Stonehenge?

August 12, 2003

Dear Straight Dope:

I just watched a segment about Stonehenge on a repeat of "In Search Of . . ." on the History Channel. The show seemed like a bunch of bunk, sucking up to the touchy-feely, crystals-and-spirits crowd (with a touch of "Chariots of the Gods" gobbledygook thrown in to further muddy the waters).  I want to know: What is the absolute, no-holds-barred Straight Dope on Stonehenge?

It's a calendar, except instead of pictures of shapely women in bikinis, it's got big chunks of rock. Alignments of different stones mark various solar or lunar events (or so some have argued).  The best known alignment, and the one we can be surest isn't mere coincidence, is for the summer solstice, a date of significance to many cultures. Stonehenge is a favorite of New Age enthusiasts, who imagine it to have been a Druid temple in the days of the early Britons. It may have been a temple, and conceivably the Druids used it as such (much as wannabe Druids do today), but the Druids didn't build it. As an archaeologist who has studied and worked briefly on excavations at Stonehenge, I can say the significance of the monument goes well beyond the puerile Druid crystals-and-spirits story. 

Impressive though it is, what we see at Stonehenge now is only a fragment of what it was in its heyday. When the final phase of construction concluded, it was a near-perfect astronomical calculator (or, again, so some have argued). Not only is Stonehenge aligned with solar and lunar events, it can be used to predict eclipses, although whether that was the intention of the builders remains controversial (see resource 3 below). But why would someone want to build it? And who built it, and when, and how?

In the early 1990s the English Heritage Scientific Dating Service assembled a group of scientists to measure, date and corroborate evidence brought to light over the previous three centuries to determine when Stonehenge was built. The scientists established that the site had been built in three phases over a period of two millennia. 

The first phase of Stonehenge was the outer ditch, which lies far outside the iconic stone structure. The ditch forms a nearly complete circle with an earthen bank on the inner side. (Now the bank is almost level with the ground due to age.) Radiocarbon dating of material found in the ditch in 1993-94 suggests it was built more than five thousand years ago, somewhat before 3000 BC (see source 1). Just inside the earthen bank are 56 small pits known as Aubrey holes after their discoverer, 17th century British antiquarian John Aubrey. It's uncertain what was in the Aubrey holes. Speculation ranges from timber posts to sacrificial ornaments.  

Organic remains in the ditch have enabled us to date it:

The main Ditch at Stonehenge was dug in a series of segments, at the base of which were deposited large numbers of antlers, many of which had been used as picks or rakes and showed heavy wear. Since these artifacts had no primary silt beneath them; they must have been deposited very soon after the Ditch was dug. It is considered that antlers would not have been kept for long before use, especially as over half (57%) came from slain deer (perhaps because a large number of antlers were needed quickly?). Consequently the digging of the Ditch can be dated to very soon after the last of the antlers was collected. (See resource 2)

As a celestial clock-tool the Henge was far from complete. The inner stone circles are where the real mystery comes in.

Phase II of construction is somewhat sketchy. Radiocarbon dating makes it reasonably certain that the second phase extended from 2800-2260 BC (92% confidence for you statisticians; see resource 1). During Phase II, after the creation of the ''Avenue," a pathway located at the northeast corner of the circle, the builders placed a ''Slaughter Stone'' just inside the confines, surrounded by four "Station Stones" set in a rectangle. A hundred feet away they positioned a ''Heel Stone'' weighing 35 tons and measuring almost 20 feet in height. This stone holds particular significance--each summer on the longest day of the year, June 21st, the sun rises directly in line with this stone when viewed from the center of the monument, giving the appearance that the sun is resting on it. On most other days of the year, one cannot see the sunrise from the center of Stonehenge (resource 2).

Two centuries after the placing of the Heel and Slaughter stones, some eighty blocks of bluestone from the Preseli Mountains in Wales were brought to the site. These stones were the lightest of the lot, but came the greatest distance. Most likely they were brought by raft around the coast of Wales to the river Avon in Bristol, then floated upstream. Once ashore, the big slabs were conveyed the relatively short distance to Salisbury plain by rolling them on timbers to the Avenue. (Some dispute this scenario, saying bluestone of the kind found at Stonehenge was available locally. Local stone and stone from the Preseli Mountains has been dated to the Pliocene Era som 650,000 years ago.)  The bluestones were placed in two concentric circles at the monument's center. 

Phase III began around 2000 BC, with work continuing episodically until 1100 BC. During this time Stonehenge assumed the form we know today. Construction was complicated and I won't attempt to recount it in detail here. The bluestones were taken down and re-erected as a smaller circle dwarfed by the larger sandstone trilithons--two large pillars with a top lintel stone--which formed a horseshoe at the center of the monument. Surrounding the trilithons were some thirty other sarsen (sandstone) stones placed upright, all capped and connected with lintels making a larger outer circle enclosing the inner horseshoe. It's worth noting the way in which the lintels were fastened together. They were connected using tongue-and-groove joints, which still hold the lintels in place today. Amazing to think this all took place before the introduction of the wheel.

How did ''they'' do it?  Here scientists including myself generally agree. When the stones were brought on site, no small feat in itself, they were laid perpendicular to holes dug into the chalk. Large wooden timbers were used to lever each stone up, whilst surely close to a hundred men pulled from the other side with ropes, slipping the stone into place. The challenge was the sheer mass of the huge stones, some 45 tons. One would think they would crush the earth on their way upright into the foundation holes. Perhaps timbers were placed beneath the stone to distribute the weight. Once the uprights were in place, each lintel was placed next to a pair of pillars, then hoisted up using wood levers and ropes, centimeter by centimeter. Scaffolding was placed underneath at each increment until the lintel was brought to the top of the pillars and slid into place. Clearly thousands of people worked on Stonehenge--it may have been the center of a large village..

As for who built Stonehenge, let's start by dispelling the myth that it was the Druids. An early champion of that idea was John Aubrey, the first to do a meticulous study of the site in the early 17th century.  Julius Caesar and others had written of a Celtic priesthood dwelling near Stonehenge at the time of the Roman conquest of Britain around 55 B.C.  But the Druids had arrived a few centuries earlier at most. At that point Stonehenge had been standing for nearly two and a half millennia and was already a ruin (resource 2).

There are several theories on who built Stonehenge. During the Neolithic period, around 3000 B.C., the ancient Britons lived in small communities. They used tools to a much greater extent than their semi-nomadic ancestors.  A people called the "beaker folk" because of their use of pottery drinking vessels resided near Stonehenge around the time construction began, and some contend that Stonehenge was their handiwork (reference 4). However, archaeological evidence for this view is scant. Others looking at the ancient tools found close to the site have surmised that the builders came from continental Europe, not Britain.  A more recent school of thought holds that the people were indigenous to the area and simply started using more complex tools (resource 3). It's possible Stonehenge was initially built to monitor the seasons for agricultural purposes, but its eventual scale and complexity suggest a highly organized culture that would have had more in mind than merely marking the beginning of planting season. Today we rely on clocks and calendars to track the passage of time. The ancient Britons had Stonehenge. 

It's likely Stonehenge had religious significance. To have built Stonehenge over a span of two millennia at considerable cost in terms of resources required an idea and a commitment shared by many. Religion has been the traditional source of such commitments. Christianity has been around less time than Stonehenge.

Whatever religious purpose if any Stonehenge may have served, an impressive amount of scientific knowledge and engineering skill went into its construction, even if you take the conservative view that the only celestial event it commemorates is the summer solstice. The builders had a sound grasp of astronomy.  Before they began their work they had determined exactly where the midsummer's sun would rise, and possibly when a great many other astronomical events would occur, and they expressed that knowledge in stone. Stonehenge is a tool, a celestial pocket watch if you will, built by a people driven by a passion to be precise.

REFERENCES Cleal, R.M.J., Walker, K.E., and Montague, R., Stonehenge in Its Landscape: The Twentieth-Century Excavations (Archaeological Report 10, 1995) Hawkins, Gerald S. and John B. White. Stonehenge Decoded, 1965. Fowles, John. The Enigma of Stonehenge, 1980 Robbins, Lawrence H., Stones, Bones, and Ancient Cities. .

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