Passage tombs are perhaps the most celebrated style of tombs, mainly due to the fantastic examples at Newgrange (County Meath), Knowth (County Meath) and Dowth (County Meath) in the Boyne Valley as well as those at Loughcrew (County Meath), which is by far the best place to experience these wonders.
The classical form of passage tomb is the cruciform style, where a long passage leads to a main chamber with 3 small chambers off, forming a cross when viewed from above. However, there are many other styles, some don't even have a passage! These other forms are with a round chamber (see Fourknocks (County Meath)), a polygonal chamber or in the form of a cross of Lorraine, which can be found at Seefin Hill (County Wicklow).
There is one form known as an undifferentiated passage tomb wherein the chamber is simply a broadening of the passage, such as at Matthewstown (County Waterford).
The passage and chamber was, once constructed, covered in a mound of earth or a stone cairn , which was in turn held in place with a kerb around its perimeter.
Perhaps what Irish passage tombs are most known for is the form of rock art more commonly called passage grave art , which can be seen in abundance along the Boyne Valley in the many cemeteries.
A compartment in a tomb in which burials were placed. In court tombs and wedge tombs a chamber is a sub-division of the burial gallery. Portal tombs have single chambers and passage tombs can have anything from one to five chambers, although usually passage tombs are considered to have a main chamber with extra subsidary chambers.
A cairn is a large pile of stones, quite often (but not always) containing a burial. Sometimes they have a kerb around the base.
Most cairns are hemi-spherical (like half a football), but the piles of stones used to cover wedge tombs, court tombs and portal tombs are also called cairns. When associated with these types of monument they are not always round, but sometimes rectangular or trapezoidal.
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).
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.
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.