In Ireland and Brittany many of the tombs are decorated with a fairly unique style of rock art and it is Ireland that has the lion's share. I once heard the figures quoted as : There are 900 examples of passage grave art in Europe and 600 of these can be found in the Boyne Valley alone. Even if these figures are inaccurate, the proportions are not far wrong.
Passage grave art consists of spirals, lozenges, serpents, oculi or eye-motifs and chevrons amongst other themes. It not only occurs inside the passages and chambers of the tombs, but also on the kerb too (see Newgrange (County Meath) and Knowth (County Meath)).
In Ireland passage grave art was thought to have gone no further south than Seefin Hill (County Wicklow), but fairly recent excavations in the late 1990s at Knockroe (County Kilkenny) changed all that.
One of the most fascinating types of remains left to us by our neolithic ancestors. Enigmatic carvings on rocks, either loose boulders or earth-fast rocks. Designs vary enormously from simple cup marks to amazing spirals, zig-zags, checker-board and lozenge patterns.
No one knows what these symbols once stood for, but many theories exist including star charts, calendars and maps. Many passage tombs are adorned with rock art, both inside the chamber and on the kerb.
A low stone used to de-lineate the divisions of a gallery. Sill stones fill the width of the space, but do not reach the roof.
A kerb is a ring of stones placed around the perimeter of a burial mound or cairn. It basically serves the purpose of a retaining wall to keep the cairn or earth in place. Kerbs are usually associated with passage tombs, but do occur on court tombs and wedge tombs too.
Sometimes on passage tombs the stones can bear decoration, such as at Newgrange (County Meath).