Stonehengineering

So many options! Boats, sleds, giants, aliens, magic…

This was going to be the title of Friday’s post, and then I realized I had written about a lot of things besides the engineering of Stonehenge, which I decided still deserved its own post.

I think of this aspect of studying Stonehenge as tackling the “what?” question, which is really the one we have the best answers for. We may not be able to reliably carbon-date nearby organic remains or put together a convincing picture of the culture that built them, but the features of the surviving structures and stones themselves can be studied and understood. This is especially true of Stonehenge 3, when most of the stone actually arrived.

First, let’s back up from “what” and consider how the stones got to the site of Stonehenge in the first place. This takes us back into the realm of the unknown, but that hasn’t stopped historians, archaeologists, engineers, and other scholars from making their own guesses. These theories are usually bounded by what we believe was possible for Neolithic humans given their probable level of technology and the features of the land around them. (Aliens are not currently considered a likely explanation, though not universally out of favor, as I was reminded when I ran across this delightful-looking book at the library last week.)

The major issue lies with the bluestones, which match those found in the Preseli Mountains of Wales, about 150 miles away. Transporting tons of stone that far is no joke even today, so it’s understandably a fascinating problem to figure out how the Neolithic builders might have done it. After all, our technology and culture have changed in ways beyond the imagination of either of our societies.

This “Stonefit Bluestone Fitness Challenge” idea is genius! I can’t believe people are paying us for the privilege of carrying these things. We’ve made 57 goats already without even counting the merchandise!

One possibility is that the bluestones were transported by water, cutting out much of the land travel by bringing the stones upriver and then the short distance inland to the Salisbury Plain. This was tested with the Millennium Stone Project, but the ropes towing the stones underwater behind the boats broke, leaving a bluestone at the bottom of the sea.

Another idea involves stone spheres that have been linked to similar standing-stone sites in Aberdeenshire and other areas. These spheres could have been used like ball bearings and lined up in a track to roll the bluestones along with much less trouble than simply hauling them along the ground.

People have come up with all kinds of ideas, including various forms and combinations of wooden log-rolling belts, tracks, and sledges. Whatever the builders used, it took a lot of time and labor, but estimates of just how much vary widely. Retired engineer Wally Wallington, for example (yes, that’s his name), has made a case for the ability of a single person to handle the huge stones without modern technology, using physics and engineering knowledge.

Once the stones reached their destination, they were raised into position, likely using wooden A-frames and ropes to bring them upright in sloped pits, which were then filled with dirt and rubble. (For some nice illustrations, check out this informative page by English Heritage!)

Beyond just getting the bluestones and sarsens to the site and in position, we know quite a bit about how they were put together. For example, the sarsens, which were used to form the circle of uprights and lintels, weren’t just a bunch of stones pushed upright with other stones laid across the top (which would’ve been difficult enough!). Instead, a few sophisticated techniques usually used in woodworking were used to join the uprights and lintels.

One of these features is the mortise and tenon joint, which uses a bump or knob (tenon) that fits exactly into a hole (mortise). Another is the tongue and groove joint, which uses the same idea, but with a groove that goes the whole length of one side of a piece and a corresponding tongue on the facing side of the next piece. Here’s a very not-to-scale, unrealistic illustration of the joints in the lintels and uprights of Stonehenge’s sarsens:

The tongue and groove lock the horizontal lintel stones together, while the mortise and tenon join each lintel to the uprights that support it. It’s not entirely clear, but some of these joints may have been finished at the last minute, once the lintels were already raised and ready to put onto the uprights.

My illustration also shows two aesthetic features of Stonehenge 3. One is the design of the upright sarsens, which are slightly wider at their tops to make sure they appear the same width all the way up from an eye-level view. This is similar to later techniques used in columns by the Greeks and other cultures.

The second feature is the shape of the lintels, which are curved so that the eye follows the circle of stones more easily. Both of these design choices are considerably more sophisticated than we would tend to expect from such an ancient monument, so it’s a useful and (I think) exciting reminder that human intelligence and ingenuity weren’t invented along with the wheel.

Obviously, I’ve only scratched the surface of what we see in these remains, because I’m trying to keep this brief. The most important thing to me is to really look at the concrete (or bluestone) results of human engineering and effort, rather than just romanticizing the mysteries of our past. Whether your interest is anthropology or engineering, I think approaching these ancient structures as scientists (albeit still with a sense of wonder) is the best way to show our respect for the people who left us these beautiful, intriguing puzzles.

[There’s a lot more to our knowledge of Stonehenge’s construction, especially in the layout of the stones! If you’re interested, you should check out how that layout changed over the centuries with this set of plans, also from English Heritage. The main Wikipedia article can also give you a lot of starting points for learning more about the engineering and construction.]