'Ball bearings' used for Stonehenge
Neolithic engineers may have used ball bearings in the construction of Stonehenge, it has been claimed.
The same technique that allows vehicles and machinery to run smoothly could have been used to transport the monument's massive standing stones more than 4,000 years ago, according to a new theory.
Scientists showed how balls placed in grooved wooden tracks would have allowed the easy movement of stones weighing many tons.
No-one has yet successfully explained how the heavy slabs used to build Stonehenge were shifted from their quarries to Salisbury Plain in Wiltshire.
Some, the "bluestones", weighed four tons each and were brought a distance of 150 miles from Pembrokeshire, Wales.
Attempts to re-enact transporting the blocks on wooden rollers or floating them on the sea have not proved convincing.
The hard surfaces and trenches needed when using rollers would also have left their mark on the landscape, but are missing.
Experts hit on the new idea after examining mysterious stone balls found near Stonehenge-like monuments in Aberdeenshire, Scotland.
About the size of a cricket ball, they are precisely fashioned to be within a millimetre of the same size. This suggests they were meant to be used together in some way rather than individually.
The Scottish stone circles are similar in form to Stonehenge, but contain some much larger stones. To test the theory, researchers from the University of Exeter constructed a model in which wooden balls were inserted into grooves dug out of timber planks.