Stonehenge has been intensively studied for centuries. Yet even now, we are still discovering new aspects of the famous site.
An archaeological 'biopsy' of the surrounding landscape has revealed a hidden network of large pits encircling the stone structure.
The study is the first extensive electromagnetic induction survey of the region, and it has helped archaeologists uncover hundreds of large pits, each over 2.4 meters (7.8 ft) wide. Some of these were most certainly made by human hands thousands of years ago.
What these large pits were used for is unknown, but given the lack of "utilitarian functions" associated with the holes, researchers suspect they were somehow related to the "long-term ceremonial structuring" of Stonehenge.
Other ancient pits, discovered near the car park of the old Stonehenge visitor center, date to about 8000 BCE and are associated with totem poles, props for hunting aurochs (a type of extinct cattle), and lunar observation.
Stonehenge itself was only built about 5,000 years ago.
"By combining new geophysical survey techniques with coring, and pin point excavation, the team has revealed some of the earliest evidence of human activity yet unearthed in the Stonehenge landscape," says archaeologist Nick Snashall, who works for the Stonehenge & Avebury World Heritage Site.
"The discovery of the largest known Early Mesolithic pit in northwest Europe shows that this was a special place for hunter-gatherer communities thousands of years before the first stones were erected."
Prehistoric pit deposits are common archaeological structures in the United Kingdom and northwest Europe, but they are usually no wider or deeper than a meter. Oval pits greater than 2.4 meters wide are very rare, but around Stonehenge and the nearby Durrington Walls Henge, they seem to be unusually concentrated.
In the recent survey of Stonehenge, geophysical sensors and direct archaeological investigation detected 415 large pits over a 2.5 km2 area. When the researchers excavated nine such pits, six were found to be human-made a long time ago, two were natural occurrences, and one was a recent agricultural deposit.
The sheer abundance of these structures is a kind of prehistoric activity not previously recognized at Stonehenge or in northwest European more generally.
The round pits range in date from the Early Mesolithic, circa 8000 BCE, to the Middle Bronze Age, circa 1300 BCE, and they are mostly concentrated on higher ground to the east and west of Stonehenge.
The oldest and largest of the pits is more than 3 meters wide and 1.85 meters deep.
"What we're seeing is not a snapshot of one moment in time. The traces we see in our data span millennia, as indicated by the seven-thousand-year timeframe between the oldest and most recent prehistoric pits we've excavated," says historian Paul Garwood from the University of Birmingham.
"From early Holocene hunter-gatherers to later Bronze Age inhabitants of farms and field systems, the archaeology we're detecting is the result of complex and ever-changing occupation of the landscape."
The ability for sensor technology to scan a landscape and reveal potential archaeological sites is giving us an unprecedented view of prehistoric landscapes.
Stonehenge is just the start.
The study was published in the Journal of Archaeological Science.