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Stonehenge Engineering

Stonehenge Engineering Photo Credit: Clipart.com

A new hypothesis explains how prehistoric people transported huge slabs of rock to Stonehenge.


Transcript

Engineering Stonehenge. I'm Bob Hirshon and this is Science Update.

Before even wheels were invented, prehistoric people moved giant rocks to Stonehenge from dozens to hundreds of miles away. Now, British archaeologists may have finally figured out how they did it. University of Exeter archaeologist Andrew Young believes they dragged the slabs along wooden tracks lined with carved wooden roller balls. He and a few students tested the technique on the smaller, four-ton stones.

Young:

We had just a handful of students. And we were able to move the blue stones of Stonehenge, just seven of us, pushing. We didn't even have to push very hard. We could go twenty miles a day.

Young suspects the slabs were actually pulled by oxen. He got the idea from identically sized stone balls found at a similar monument in Scotland. A chalk model of the same type of ball at Stonehenge suggests the technique caught on. I'm Bob Hirshon, for AAAS, the science society.


Making Sense of the Research

Stonehenge, a stone monument in the English countryside, has fascinated scientists and lay people for ages. It was built and refined by Stone Age people over a period of many centuries, starting around 3000 BC and continuing until about 1600 BC, and remained in use until about 500 BC. The most striking feature of the monument is its circle of giant stone slabs, weighing four to forty tons. Many of the slabs stand vertically, with another slab topping two vertical stones like a door frame. 

By analyzing the stones' composition, scientists have long known that some of them, called bluestones, could have come only from the rocky coast of Wales, 160 miles from the Stonehenge site. That means they were somehow transported over that distance, without the aid of carts, wagons, or anything with wheels—because wheels hadn't been invented yet. Lifting the massive stones would have been backbreaking for even a large number of people, to say nothing of carrying them over hill and dale for days on end. Even a team of oxen would be hard pressed to drag the stones across the ground without some kind of assistance. 

So how did they do it? That's a question scientists have asked for many, many years, and although many theories have been put forward, Dr. Young says that none of them has been very satisfying. In a nutshell, some of them involved constructing tracks that would have left some kind of mark in the landscape, and others required too much manpower to be practical.

Young got the idea for this method while studying a similar stone circle near Aberdeen, Scotland. There, archaeologists had found dozens of carved stone balls among the ruins. Young studied the balls and noticed that they were almost exactly the same size—within a millimeter of each other in diameter, in fact. This would have been difficult and time-consuming to do using only stone tools. So, Young reasoned that they must be the same size for an important reason, probably because they were meant to be used together in some kind of system.

Then he came up with the idea for the ball-based tracks. He laid the balls down on the ground in a straight line, with wooden tracks on either side to keep them from rolling away. Doing that, he found that he could roll heavy objects across them quite easily. 

But was it good enough to move the rocks of Stonehenge? To find out, Young built a larger track, using wooden balls of the same size, and got some of the same four-ton bluestones that are found at Stonehenge. He found that moving the enormous stone slabs didn't take much effort, using only six or seven people—compared with the hundreds it took to drag stones along previous researchers' model tracks. What's more, the tracks didn't leave a lasting impression on the ground, which would explain why there's no evidence of them along the route. 

Young imagines that the actual Stone Age people may have used oxen to pull the slabs. In fact, ox bones have been found at Stonehenge, and appear to have been burned in some kind of ritual, perhaps a sacrifice to celebrate the achievement. He also notes that the Stone Age engineers wouldn't have needed to lay one track all the way from Wales to the Stonehenge site. Instead, they could have just put down a short stretch of track, and as the oxen moved along it, human workers could easily have picked up the track and balls from the back end and added them to the front. 

So, why aren't there carved stone balls at Stonehenge itself? Young says that unlike the Stone Age people in Scotland, the people who lived around Stonehenge made many things out of wood, since there was plenty of high-quality wood in the area. However, wood artifacts can't normally survive in the English climate over thousands of years. In fact, they usually can be found only in places like the bottom of peat bogs, where low-oxygen conditions protect them from decomposing. He notes that although they have found thousands of stone axe heads from the time period, fewer than a dozen wooden axe handles have survived to the present day, in far from perfect condition. Given those odds, the chance that a wooden stone ball would still be around in the 21st century are extremely slim. 

However, his team did find a chalk ball at Stonehenge, about the size and shape of the Aberdeen stone balls. Young says that over time, Stone Age people from different areas did interact with one another. So it's quite possible that someone came from Aberdeen, saw their track system, made a model ball out of chalk, and then had the local woodworkers carve many more copies. 

Now try and answer these questions:

  1. Why is the construction of Stonehenge mysterious?
  2. Why have past hypotheses not satisfactorily explained how it was built?
  3. How does the author explain the absence of wooden balls at the Stonehenge site?
  4. Why was it important to build a life-size model of the track system?

For Educators

In the National Geographic Xpeditions lesson plan Seasons: Why It's Essential, students investigate theories about the function of Stonehenge and other ancient monuments as a way of tracking and commemorating the seasons.

In the student interactive 300 Spartans: The Bridge Over the Hellespont, students re-create another marvel of ancient engineering: a pontoon bridge Xerxes built over the Hellespont in ancient Greece.


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