Callanish IV - the Romans never came here, but the antiquarian numbering scheme catalogues this monument as the fourth of the Callanish group - lies near the small settlement of Garynahine on the west coast of Lewis. At its centre is a dilapidated cairn; to the southwest, the stone footprint of a shieling, the seasonal summer hut a Hebridean shepherd would have built to live in while watching cattle on the hill. Of the original stones, five remain upright. The others may have fallen and been buried in the deepening peat, or they may have been cleared away over centuries. What is visible aboveground is only part of what is here. Nobody yet knows how much more.

Callanish IV became a scheduled monument in 1992, under Scottish law that gives the highest legal protection to sites of national importance. The protected area is irregular - the longest aspect runs 410 metres north-south - and it covers far more than the visible cairn. Historic Environment Scotland's statement of importance reads, in part: 'The undisturbed deep peat around it gives it the potential for recovery of information regarding contemporary landuse and economy, and possibly other structural evidence... Together, this complex is one of the most remarkable Neolithic/Bronze Age site assemblages in NW Europe.' The peat, in other words, is the archive. Disturb it and you lose what you came to find. Protecting Callanish IV is partly an act of refusal: do not dig until you can read.

Callanish IV is one of more than a dozen stone circles, alignments, single stones and cairns scattered across this corner of west Lewis - a sacred landscape laid out across several square kilometres around the village of Calanais. The main site, Callanish I, is one of the most spectacular Neolithic monuments in Europe, a cross-shaped arrangement of standing stones whose construction began around 2900 BC. Callanish II and III lie to its south, smaller and less famous. Callanish IV sits further south still, then V, VI, VII, VIII... There is no full agreement on what the group did or meant, but the sightlines across the moor are clearly intentional. Standing at Callanish IV at twilight, you can sometimes see the silhouettes of the other circles on neighbouring ridges. They were not built in isolation. They were built in conversation.