Construction work was halted last week following the discovery of a segment of wall on the site. The find turned up on the last day of a watching brief – where archaeologists monitor operations to ensure no archaeological remains are disturbed or damaged.
The site lies a few hundred yards to the north of the stone circle, by the shore of the Harray loch and on the Sandwick side of the Ness of Brodgar.
Formerly occupied by Ned Spence, the site was chosen because disruptions caused by more recent activity meant that siting a car park there would have a minimal impact on the Ness’s archaeology.
But then the ancient masonry turned up on the very edge of the construction site.
Orkney Archaeology Trust’s projects manager, Nick Card, explained: “We originally thought it might be some piece of medieval ruin, but it soon became clear that what we had was extremely well-built and appeared to be much older.
“The structure was right at the very edge of the proposed car park and, although pieces had been removed in the more recent past, it turned out to be a massive, beautifully built wall about one metre across and surviving in parts to up to about a foot high.
“Going back to the aerial photographs we have of the area, and studying them closer, it would appear what we originally thought was a geological feature could actually be a prehistoric wall continuing out across the ness in a massive arc.
“It’s early days yet,” he said, “but the wall seems to have formed a huge circular enclosure, with an estimated diameter of 100 metres.
“This, together with its proximity to the Ring of Brodgar, is very interesting and potentially incredibly important to our understanding of the area and its use.”
To give an idea of the size of the enclosure, the nearby Ring of Brodgar has a diameter of 103.6 metres.
The archaeologists plan to use resistivity scans to provide a clear picture of the extent of the construction. This involves passing an electrical current through the ground at regular points on a survey grid. Because electrical resistance in the soil varies, and is affected by the presence of archaeological features, the patterns of resistance in the soil can be recorded, plotted and interpreted.
Meanwhile, to preserve the ancient wall, the car park is being moved, by a few metres, to an area clear of archaeology.