Before dawn this morning, I watched NOVA. It appears as though the massive stones for Stonehenge were hauled on a plank set over a grooved track using ball bearings chiseled from stone: Here's some transcript from the episode:

NARRATOR: Masons may have roughly shaped the sarsens at the quarry site, using pounding stones. But they left few clues to how they moved and raised giant stones.

LEADER (Dramatization of Stonehenge masons gathering stones): One, two, three, four!

NARRATOR: So researchers have experimented.

Stone Age Britain did not have the wheel, but people may have pulled large stones over rollers made of tree trunks. Perhaps they laid timber tracks and slathered them with grease. A wooden sled with a keel would have kept the stone centered over the tracks. Raising a giant stone involved somehow tipping it into a giant hole. Lintels may have been pulled up ramps and levered into place. All these techniques are plausible. There's just no evidence they were actually used.

Now there's a new theory.

Andrew Young became obsessed with carved stone balls during graduate work at the University of Exeter. Some of these prehistoric objects are elaborately engraved, but many are unadorned.

Most have been found in northeast Scotland, an area known for its stone circles. These artifacts defy explanation.

ANDREW YOUNG (The University of Exeter): People had said they might be weapons or for throwing or, uh, possibly pounding vegetables, kinds of things that you could do with portable stone objects. Nothing that anybody had really said about them satisfied my question: "What are they for?"

NARRATOR: Young taught himself to carve replicas and pondered one strange fact. Many carved balls, engraved and plain, have exactly the same diameter.

ANDY YOUNG: Large numbers are identical in size, to the millimeter. And why would they need to be identical in size? And that just gave me that eureka moment. "Wow. If you're going to use them as a wheel you need them to be the same size."

BRUCE BRADLEY: Andy brought this theory to me. I was astounded, because it just made sense. It's just so obvious. Why didn't somebody think of this before?

NOVA | Secrets of Stonehenge