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.
