Some of the volcanic bluestones in the inner ring of Stonehenge officially match an outcrop in Wales that’s 160 miles (257 kilometers) from the world-famous site, geologists announced this week.
The discovery leaves two big ideas standing about how the massive pieces of the monument arrived at Salisbury Plain: entirely by human hand, or partly by glacier.
As it looks today, 5,000-year-old Stonehenge has an outer ring of 20- to 30-ton sandstone blocks and an inner ring and horseshoe of 3- to 5-ton volcanic bluestone blocks.
The monument’s larger outer blocks, called the Sarsen stones, were likely quarried some 20 to 30 miles (32 to 48 kilometers) away in what’s now England, where sandstone is a common material.
The origin of the bluestones, however, has weighed heavy on the hearts of archaeologists. Rocks resembling the material under a microscope haven’t been found anywhere relatively near Stonehenge—at least until now.
Pinpointing the stones’ origins is crucial to understanding how so many heavy hunks of rock made their way to the open plain where Stonehenge now stands.
“There’s no way of explaining how these stones were transported without knowing where they came from,” said study co-author Robert Ixer of the University of Leicester in the U.K.