England’s most famous prehistoric ruin draws visitors from across the globe. Today’s Druids gather at Stonehenge to witness the midsummer sunrise.
Archaeologists believe Neolithic settlers constructed Stonehenge in several stages. Deep pits (called Aubrey holes after 17th-century antiquarian John Aubrey) within the enclosure may have held timber posts.
Granite “bluestones” and sandstone pillars form two circles, a horseshoe, and an altar. Scientists don’t know what the site was used for, but it seems to have marked the summer solstice and midwinter sunset.
What is so special about Stonehenge?
Stonehenge has sparked the imaginations of visitors for generations. It has inspired legends of giants, human sacrifice, and even alien landings. Its purpose remains a mystery, although scholars have suggested it was a solar or lunar calendar or a monument to a specific god or king. Its positioning at the solstices (the longest and shortest days of the year) is especially significant, with the sun appearing to be directly above the Heel Stone during the summer solstice and directly over the Altar stone at the winter solstice. Its location at the center of a precinct also suggests it was a place for ritual.
Scientists still debate how the monument came to be, but most agree that it was constructed in stages by distinct tribes. Some believe that industrious Neolithic agrarians began the work, while later groups with more advanced tools and a more communal lifestyle left their mark on the site.
The Sarsens
The outer circle of sarsen stones, which stood up to 7 meters high, and the lintels on the inner trilithon are among the surviving parts of Stonehenge. People erected them in the form of a horseshoe, with each stone pair having a lintel connecting them.
Sarsen is found in scattered deposits across southern Britain, where it formed when sand and gravel were deposited over chalk sea bed layers. Prehistoric monument builders favored the stone, and it was later used for Roman villas, medieval churches, and roads.
To identify the source of a sarsen stone, the team needed to compare its geochemistry with that of individual outcrops. However, tearing a sample out of one of the upstanding sarsens (or orthostats) would have been near sacrilege. To avoid this, the team tested the geochemistry of a core taken from the base of Stone 58. The results suggest that most sarsens at Stonehenge, except two outliers, came from the same area.
The Bluestones
A handful of stone chips and a scrap pile of charred wood may not sound like treasure to the archaeologists who discovered them at Stonehenge, but those pieces of evidence are important. They confirm that Neolithic people believed the bluestones brought from Wales possessed healing properties.
It was a chance discovery in 2008. Tim Darvill and Geoff Wainwright were conducting the first excavations of the monument’s inner area in 40 years. While they were digging, a colleague sent them a shoebox full of rock fragments. One of those fragments had a familiar look to geologist Rob Ixer, who knew it was made from the same rock as the stone in a monument at Craig Rhos-y-Felin in the Preseli Hills in Wales. He sectioned the stone and found that it matched five of the fragments in the Shoebox. That was a huge revelation. It changed the way that geologists think about how Stonehenge came to be.
The Altar Stone
Although we know that the Sarsen stones came from Marlborough Downs about 20 kilometers to the north of Stonehenge and the bluestones were sourced in the Preseli hills of Pembrokeshire some 140 kilometers south of the site the provenance of the Altar Stone remains a mystery. This is because it’s made of a different type of rock, a grey-green micaceous sandstone.
Mica is known to glitter when it’s wet which gives this particular sandstone its name. It’s a strange rock to use at Stonehenge, but it has an important role as one of the six Sacred Stones that is used to identify the positions of the Vertices.
The latest research has suggested that the Altar Stone may not come from Wales after all. A petrographic analysis of a debitage fragment assumed to be the Altar Stone (Reference Ixer and Turner 2006) has shown that it is not derived from the Cosheston Subgroup, and the researchers suggest further investigation of northern England and Scotland.
