A previously unknown stone circle lies buried beneath one of Scotland’s ceremonial moors

Geophysical survey has revealed a previously unknown stone circle buried beneath Machrie Moor, one of Scotland’s most significant ceremonial landscapes, on the Isle of Arran. Historic Environment Scotland archaeologists detected 12 circular pit-like features arranged in a ring, with room for two more settings, forming a monument the agency has named Machrie 12 — invisible above ground and identified only through underground scanning. The find joins six stone circles already known at the site and appears to be the largest of any of them.

The survey that found it was not a search for buried treasure. It began as a practical response to visitors wearing an informal dirt path into the peat between two existing circles, and it doubled as a test of whether standard geophysical equipment could work reliably in a peat bog, a setting where the technique has traditionally performed poorly.

How Machrie 12 Was Found Underground

Nick Hannon, Historic Environment Scotland’s Senior Heritage Recording Manager for geophysical survey, has said the equipment used at Machrie Moor does not produce results instantly. The team downloads data in the field, then processes and interprets it back at a desk, which is the point at which the new circle first became visible — not the moment the instrument passed over the ground. The technique, called gradiometry, measures the Earth’s magnetic field rather than passing an electric current through the soil, so it keeps working in conditions that would defeat other methods; the only real limitation Hannon cited was a thunderstorm, avoided for the survey crew’s safety rather than any effect on the readings.

That distinction mattered on a peat moor. Earth Resistance survey, a more common geophysical technique that passes a low-voltage current through the ground, struggles when soil is especially wet or dry, a real risk across a bog. Gradiometry’s reliance on magnetic readings sidesteps that problem, which is part of why Historic Environment Scotland’s own account of the project treats the choice of method as a finding in its own right, not just a means to one.

A Ring Larger Than Six Known Circles

Machrie 12 measures roughly 28 by 25 meters and is slightly ovoid, a shape the agency says is not unusual for stone circles of this period. That makes it the largest known circle at Machrie Moor, larger than the six previously identified monuments the site is already known for — Circles 1, 2, 3, 4, 5 and 11, according to HeritageDaily’s report on the find.

No stones or timbers from Machrie 12 survive above ground, which is why archaeologists describe it only in terms of the buried anomalies the survey mapped: a dozen roughly evenly spaced pits or postholes forming a ring, with two gaps large enough to have held additional settings that may never have been built or may not have survived.

Why the Site Was Surveyed

The immediate trigger was erosion. Visitors have long walked informally between Circles 2 and 3, where no marked path exists, wearing “desire lines” into the peat that Historic Environment Scotland wanted to assess before more damage occurred. Surveying the ground first meant any archaeology hidden beneath those informal routes could be identified and protected rather than trampled without anyone knowing it was there.

The agency’s original announcement of the find, first shared in June 2026, frames the discovery as confirmation that the moor still has more to reveal even after generations of visitors, researchers and archaeologists have walked its surface. Machrie 12 sits directly between Circles 2 and 3, on the exact ground the erosion survey was designed to check.

Thousands of Years of Ritual and Farming

Machrie Moor’s occupation stretches back to roughly 7,800 BC, when Mesolithic hunter-gatherers began clearing the area’s woodland through controlled burning. Neolithic farmers later worked the land and kept livestock, and the earliest ritual activity at the site — pits dug where Circle 11 now stands — dates to this same period, before timber circles and organized field systems appeared. The stone circles themselves were built around 2,000 BC, a period that coincides with reduced evidence of farming, suggesting the moor’s role may have shifted toward ceremony and gathering rather than subsistence.

Bronze Age communities later returned to farming at a larger scale, built roundhouses nearby, and reused some monuments for burials, before deteriorating soils and spreading peat gradually buried and preserved much of what the recent survey has now brought back into view. Even the visible circles carry later layers: at Circle 2, two stones lying on the ground appear to have been worked into millstones sometime after the medieval period, evidence that the moor kept being used long after its original ceremonial purpose faded.

Whether Machrie 12 aligns with the midsummer sunrise the way parts of the wider landscape appear to is impossible to confirm, since no standing stones or timbers survive to test the alignment against, unlike the circles that remain visible above ground today. Dr Hazel Blake, who operated the wheeled gradiometry frame beside Circle 3 during the survey, is credited alongside Hannon with the fieldwork that turned an unmarked stretch of peat into the moor’s newest — and largest — known monument.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.